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  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

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  * published by the Free Software Foundation.  Oracle designates this

  * particular file as subject to the "Classpath" exception as provided

  * by Oracle in the LICENSE file that accompanied this code.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

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 package java.net;

 import java.io.IOException;

 import java.io.InvalidObjectException;

 import java.io.ObjectInputStream;

 import java.io.ObjectOutputStream;

 import java.io.Serializable;

 import java.lang.Character;             // for javadoc

 import java.lang.NullPointerException;  // for javadoc

 /**

  * Represents a Uniform Resource Identifier (URI) reference.

  *

  * <p> Aside from some minor deviations noted below, an instance of this

  * class represents a URI reference as defined by

  * <a href="http://www.ietf.org/rfc/rfc2396.txt"><i>RFC&nbsp;2396: Uniform

  * Resource Identifiers (URI): Generic Syntax</i></a>, amended by <a

  * href="http://www.ietf.org/rfc/rfc2732.txt"><i>RFC&nbsp;2732: Format for

  * Literal IPv6 Addresses in URLs</i></a>. The Literal IPv6 address format

  * also supports scope_ids. The syntax and usage of scope_ids is described

  * <a href="Inet6Address.html#scoped">here</a>.

  * This class provides constructors for creating URI instances from

  * their components or by parsing their string forms, methods for accessing the

  * various components of an instance, and methods for normalizing, resolving,

  * and relativizing URI instances.  Instances of this class are immutable.

  *

  *

  * <h4> URI syntax and components </h4>

  *

  * At the highest level a URI reference (hereinafter simply "URI") in string

  * form has the syntax

  *

  * <blockquote>

  * [<i>scheme</i><tt><b>:</b></tt><i></i>]<i>scheme-specific-part</i>[<tt><b>#</b></tt><i>fragment</i>]

  * </blockquote>

  *

  * where square brackets [...] delineate optional components and the characters

  * <tt><b>:</b></tt> and <tt><b>#</b></tt> stand for themselves.

  *

  * <p> An <i>absolute</i> URI specifies a scheme; a URI that is not absolute is

  * said to be <i>relative</i>.  URIs are also classified according to whether

  * they are <i>opaque</i> or <i>hierarchical</i>.

  *

  * <p> An <i>opaque</i> URI is an absolute URI whose scheme-specific part does

  * not begin with a slash character (<tt>'/'</tt>).  Opaque URIs are not

  * subject to further parsing.  Some examples of opaque URIs are:

  *

  * <blockquote><table cellpadding=0 cellspacing=0 summary="layout">

  * <tr><td><tt>mailto:java-net@java.sun.com</tt><td></tr>

  * <tr><td><tt>news:comp.lang.java</tt><td></tr>

  * <tr><td><tt>urn:isbn:096139210x</tt></td></tr>

  * </table></blockquote>

  *

  * <p> A <i>hierarchical</i> URI is either an absolute URI whose

  * scheme-specific part begins with a slash character, or a relative URI, that

  * is, a URI that does not specify a scheme.  Some examples of hierarchical

  * URIs are:

  *

  * <blockquote>

  * <tt>http://java.sun.com/j2se/1.3/</tt><br>

  * <tt>docs/guide/collections/designfaq.html#28</tt><br>

  * <tt>../../../demo/jfc/SwingSet2/src/SwingSet2.java</tt><br>

  * <tt>file:///~/calendar</tt>

  * </blockquote>

  *

  * <p> A hierarchical URI is subject to further parsing according to the syntax

  *

  * <blockquote>

  * [<i>scheme</i><tt><b>:</b></tt>][<tt><b>//</b></tt><i>authority</i>][<i>path</i>][<tt><b>?</b></tt><i>query</i>][<tt><b>#</b></tt><i>fragment</i>]

  * </blockquote>

  *

  * where the characters <tt><b>:</b></tt>, <tt><b>/</b></tt>,

  * <tt><b>?</b></tt>, and <tt><b>#</b></tt> stand for themselves.  The

  * scheme-specific part of a hierarchical URI consists of the characters

  * between the scheme and fragment components.

  *

  * <p> The authority component of a hierarchical URI is, if specified, either

  * <i>server-based</i> or <i>registry-based</i>.  A server-based authority

  * parses according to the familiar syntax

  *

  * <blockquote>

  * [<i>user-info</i><tt><b>@</b></tt>]<i>host</i>[<tt><b>:</b></tt><i>port</i>]

  * </blockquote>

  *

  * where the characters <tt><b>@</b></tt> and <tt><b>:</b></tt> stand for

  * themselves.  Nearly all URI schemes currently in use are server-based.  An

  * authority component that does not parse in this way is considered to be

  * registry-based.

  *

  * <p> The path component of a hierarchical URI is itself said to be absolute

  * if it begins with a slash character (<tt>'/'</tt>); otherwise it is

  * relative.  The path of a hierarchical URI that is either absolute or

  * specifies an authority is always absolute.

  *

  * <p> All told, then, a URI instance has the following nine components:

  *

  * <blockquote><table summary="Describes the components of a URI:scheme,scheme-specific-part,authority,user-info,host,port,path,query,fragment">

  * <tr><th><i>Component</i></th><th><i>Type</i></th></tr>

  * <tr><td>scheme</td><td><tt>String</tt></td></tr>

  * <tr><td>scheme-specific-part&nbsp;&nbsp;&nbsp;&nbsp;</td><td><tt>String</tt></td></tr>

  * <tr><td>authority</td><td><tt>String</tt></td></tr>

  * <tr><td>user-info</td><td><tt>String</tt></td></tr>

  * <tr><td>host</td><td><tt>String</tt></td></tr>

  * <tr><td>port</td><td><tt>int</tt></td></tr>

  * <tr><td>path</td><td><tt>String</tt></td></tr>

  * <tr><td>query</td><td><tt>String</tt></td></tr>

  * <tr><td>fragment</td><td><tt>String</tt></td></tr>

  * </table></blockquote>

  *

  * In a given instance any particular component is either <i>undefined</i> or

  * <i>defined</i> with a distinct value.  Undefined string components are

  * represented by <tt>null</tt>, while undefined integer components are

  * represented by <tt>-1</tt>.  A string component may be defined to have the

  * empty string as its value; this is not equivalent to that component being

  * undefined.

  *

  * <p> Whether a particular component is or is not defined in an instance

  * depends upon the type of the URI being represented.  An absolute URI has a

  * scheme component.  An opaque URI has a scheme, a scheme-specific part, and

  * possibly a fragment, but has no other components.  A hierarchical URI always

  * has a path (though it may be empty) and a scheme-specific-part (which at

  * least contains the path), and may have any of the other components.  If the

  * authority component is present and is server-based then the host component

  * will be defined and the user-information and port components may be defined.

  *

  *

  * <h4> Operations on URI instances </h4>

  *

  * The key operations supported by this class are those of

  * <i>normalization</i>, <i>resolution</i>, and <i>relativization</i>.

  *

  * <p> <i>Normalization</i> is the process of removing unnecessary <tt>"."</tt>

  * and <tt>".."</tt> segments from the path component of a hierarchical URI.

  * Each <tt>"."</tt> segment is simply removed.  A <tt>".."</tt> segment is

  * removed only if it is preceded by a non-<tt>".."</tt> segment.

  * Normalization has no effect upon opaque URIs.

  *

  * <p> <i>Resolution</i> is the process of resolving one URI against another,

  * <i>base</i> URI.  The resulting URI is constructed from components of both

  * URIs in the manner specified by RFC 2396, taking components from the

  * base URI for those not specified in the original.  For hierarchical URIs,

  * the path of the original is resolved against the path of the base and then

  * normalized.  The result, for example, of resolving

  *

  * <blockquote>

  * <tt>docs/guide/collections/designfaq.html#28&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</tt>(1)

  * </blockquote>

  *

  * against the base URI <tt>http://java.sun.com/j2se/1.3/</tt> is the result

  * URI

  *

  * <blockquote>

  * <tt>http://java.sun.com/j2se/1.3/docs/guide/collections/designfaq.html#28</tt>

  * </blockquote>

  *

  * Resolving the relative URI

  *

  * <blockquote>

  * <tt>../../../demo/jfc/SwingSet2/src/SwingSet2.java&nbsp;&nbsp;&nbsp;&nbsp;</tt>(2)

  * </blockquote>

  *

  * against this result yields, in turn,

  *

  * <blockquote>

  * <tt>http://java.sun.com/j2se/1.3/demo/jfc/SwingSet2/src/SwingSet2.java</tt>

  * </blockquote>

  *

  * Resolution of both absolute and relative URIs, and of both absolute and

  * relative paths in the case of hierarchical URIs, is supported.  Resolving

  * the URI <tt>file:///~calendar</tt> against any other URI simply yields the

  * original URI, since it is absolute.  Resolving the relative URI (2) above

  * against the relative base URI (1) yields the normalized, but still relative,

  * URI

  *

  * <blockquote>

  * <tt>demo/jfc/SwingSet2/src/SwingSet2.java</tt>

  * </blockquote>

  *

  * <p> <i>Relativization</i>, finally, is the inverse of resolution: For any

  * two normalized URIs <i>u</i> and&nbsp;<i>v</i>,

  *

  * <blockquote>

  *   <i>u</i><tt>.relativize(</tt><i>u</i><tt>.resolve(</tt><i>v</i><tt>)).equals(</tt><i>v</i><tt>)</tt>&nbsp;&nbsp;and<br>

  *   <i>u</i><tt>.resolve(</tt><i>u</i><tt>.relativize(</tt><i>v</i><tt>)).equals(</tt><i>v</i><tt>)</tt>&nbsp;&nbsp;.<br>

  * </blockquote>

  *

  * This operation is often useful when constructing a document containing URIs

  * that must be made relative to the base URI of the document wherever

  * possible.  For example, relativizing the URI

  *

  * <blockquote>

  * <tt>http://java.sun.com/j2se/1.3/docs/guide/index.html</tt>

  * </blockquote>

  *

  * against the base URI

  *

  * <blockquote>

  * <tt>http://java.sun.com/j2se/1.3</tt>

  * </blockquote>

  *

  * yields the relative URI <tt>docs/guide/index.html</tt>.

  *

  *

  * <h4> Character categories </h4>

  *

  * RFC 2396 specifies precisely which characters are permitted in the

  * various components of a URI reference.  The following categories, most of

  * which are taken from that specification, are used below to describe these

  * constraints:

  *

  * <blockquote><table cellspacing=2 summary="Describes categories alpha,digit,alphanum,unreserved,punct,reserved,escaped,and other">

  *   <tr><th valign=top><i>alpha</i></th>

  *       <td>The US-ASCII alphabetic characters,

  *        <tt>'A'</tt>&nbsp;through&nbsp;<tt>'Z'</tt>

  *        and <tt>'a'</tt>&nbsp;through&nbsp;<tt>'z'</tt></td></tr>

  *   <tr><th valign=top><i>digit</i></th>

  *       <td>The US-ASCII decimal digit characters,

  *       <tt>'0'</tt>&nbsp;through&nbsp;<tt>'9'</tt></td></tr>

  *   <tr><th valign=top><i>alphanum</i></th>

  *       <td>All <i>alpha</i> and <i>digit</i> characters</td></tr>

  *   <tr><th valign=top><i>unreserved</i>&nbsp;&nbsp;&nbsp;&nbsp;</th>

  *       <td>All <i>alphanum</i> characters together with those in the string

  *        <tt>"_-!.~'()*"</tt></td></tr>

  *   <tr><th valign=top><i>punct</i></th>

  *       <td>The characters in the string <tt>",;:$&+="</tt></td></tr>

  *   <tr><th valign=top><i>reserved</i></th>

  *       <td>All <i>punct</i> characters together with those in the string

  *        <tt>"?/[]@"</tt></td></tr>

  *   <tr><th valign=top><i>escaped</i></th>

  *       <td>Escaped octets, that is, triplets consisting of the percent

  *           character (<tt>'%'</tt>) followed by two hexadecimal digits

  *           (<tt>'0'</tt>-<tt>'9'</tt>, <tt>'A'</tt>-<tt>'F'</tt>, and

  *           <tt>'a'</tt>-<tt>'f'</tt>)</td></tr>

  *   <tr><th valign=top><i>other</i></th>

  *       <td>The Unicode characters that are not in the US-ASCII character set,

  *           are not control characters (according to the {@link

  *           java.lang.Character#isISOControl(char) Character.isISOControl}

  *           method), and are not space characters (according to the {@link

  *           java.lang.Character#isSpaceChar(char) Character.isSpaceChar}

  *           method)&nbsp;&nbsp;<i>(<b>Deviation from RFC 2396</b>, which is

  *           limited to US-ASCII)</i></td></tr>

  * </table></blockquote>

  *

  * <p><a name="legal-chars"></a> The set of all legal URI characters consists of

  * the <i>unreserved</i>, <i>reserved</i>, <i>escaped</i>, and <i>other</i>

  * characters.

  *

  *

  * <h4> Escaped octets, quotation, encoding, and decoding </h4>

  *

  * RFC 2396 allows escaped octets to appear in the user-info, path, query, and

  * fragment components.  Escaping serves two purposes in URIs:

  *

  * <ul>

  *

  *   <li><p> To <i>encode</i> non-US-ASCII characters when a URI is required to

  *   conform strictly to RFC&nbsp;2396 by not containing any <i>other</i>

  *   characters.  </p></li>

  *

  *   <li><p> To <i>quote</i> characters that are otherwise illegal in a

  *   component.  The user-info, path, query, and fragment components differ

  *   slightly in terms of which characters are considered legal and illegal.

  *   </p></li>

  *

  * </ul>

  *

  * These purposes are served in this class by three related operations:

  *

  * <ul>

  *

  *   <li><p><a name="encode"></a> A character is <i>encoded</i> by replacing it

  *   with the sequence of escaped octets that represent that character in the

  *   UTF-8 character set.  The Euro currency symbol (<tt>'&#92;u20AC'</tt>),

  *   for example, is encoded as <tt>"%E2%82%AC"</tt>.  <i>(<b>Deviation from

  *   RFC&nbsp;2396</b>, which does not specify any particular character

  *   set.)</i> </p></li>

  *

  *   <li><p><a name="quote"></a> An illegal character is <i>quoted</i> simply by

  *   encoding it.  The space character, for example, is quoted by replacing it

  *   with <tt>"%20"</tt>.  UTF-8 contains US-ASCII, hence for US-ASCII

  *   characters this transformation has exactly the effect required by

  *   RFC&nbsp;2396. </p></li>

  *

  *   <li><p><a name="decode"></a>

  *   A sequence of escaped octets is <i>decoded</i> by

  *   replacing it with the sequence of characters that it represents in the

  *   UTF-8 character set.  UTF-8 contains US-ASCII, hence decoding has the

  *   effect of de-quoting any quoted US-ASCII characters as well as that of

  *   decoding any encoded non-US-ASCII characters.  If a <a

  *   href="../nio/charset/CharsetDecoder.html#ce">decoding error</a> occurs

  *   when decoding the escaped octets then the erroneous octets are replaced by

  *   <tt>'&#92;uFFFD'</tt>, the Unicode replacement character.  </p></li>

  *

  * </ul>

  *

  * These operations are exposed in the constructors and methods of this class

  * as follows:

  *

  * <ul>

  *

  *   <li><p> The {@link #URI(java.lang.String) <code>single-argument

  *   constructor</code>} requires any illegal characters in its argument to be

  *   quoted and preserves any escaped octets and <i>other</i> characters that

  *   are present.  </p></li>

  *

  *   <li><p> The {@link

  *   #URI(java.lang.String,java.lang.String,java.lang.String,int,java.lang.String,java.lang.String,java.lang.String)

  *   <code>multi-argument constructors</code>} quote illegal characters as

  *   required by the components in which they appear.  The percent character

  *   (<tt>'%'</tt>) is always quoted by these constructors.  Any <i>other</i>

  *   characters are preserved.  </p></li>

  *

  *   <li><p> The {@link #getRawUserInfo() getRawUserInfo}, {@link #getRawPath()

  *   getRawPath}, {@link #getRawQuery() getRawQuery}, {@link #getRawFragment()

  *   getRawFragment}, {@link #getRawAuthority() getRawAuthority}, and {@link

  *   #getRawSchemeSpecificPart() getRawSchemeSpecificPart} methods return the

  *   values of their corresponding components in raw form, without interpreting

  *   any escaped octets.  The strings returned by these methods may contain

  *   both escaped octets and <i>other</i> characters, and will not contain any

  *   illegal characters.  </p></li>

  *

  *   <li><p> The {@link #getUserInfo() getUserInfo}, {@link #getPath()

  *   getPath}, {@link #getQuery() getQuery}, {@link #getFragment()

  *   getFragment}, {@link #getAuthority() getAuthority}, and {@link

  *   #getSchemeSpecificPart() getSchemeSpecificPart} methods decode any escaped

  *   octets in their corresponding components.  The strings returned by these

  *   methods may contain both <i>other</i> characters and illegal characters,

  *   and will not contain any escaped octets.  </p></li>

  *

  *   <li><p> The {@link #toString() toString} method returns a URI string with

  *   all necessary quotation but which may contain <i>other</i> characters.

  *   </p></li>

  *

  *   <li><p> The {@link #toASCIIString() toASCIIString} method returns a fully

  *   quoted and encoded URI string that does not contain any <i>other</i>

  *   characters.  </p></li>

  *

  * </ul>

  *

  *

  * <h4> Identities </h4>

  *

  * For any URI <i>u</i>, it is always the case that

  *

  * <blockquote>

  * <tt>new URI(</tt><i>u</i><tt>.toString()).equals(</tt><i>u</i><tt>)</tt>&nbsp;.

  * </blockquote>

  *

  * For any URI <i>u</i> that does not contain redundant syntax such as two

  * slashes before an empty authority (as in <tt>file:///tmp/</tt>&nbsp;) or a

  * colon following a host name but no port (as in

  * <tt>http://java.sun.com:</tt>&nbsp;), and that does not encode characters

  * except those that must be quoted, the following identities also hold:

  *

  * <blockquote>

  * <tt>new URI(</tt><i>u</i><tt>.getScheme(),<br>

  * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</tt><i>u</i><tt>.getSchemeSpecificPart(),<br>

  * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</tt><i>u</i><tt>.getFragment())<br>

  * .equals(</tt><i>u</i><tt>)</tt>

  * </blockquote>

  *

  * in all cases,

  *

  * <blockquote>

  * <tt>new URI(</tt><i>u</i><tt>.getScheme(),<br>

  * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</tt><i>u</i><tt>.getUserInfo(),&nbsp;</tt><i>u</i><tt>.getAuthority(),<br>

  * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</tt><i>u</i><tt>.getPath(),&nbsp;</tt><i>u</i><tt>.getQuery(),<br>

  * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</tt><i>u</i><tt>.getFragment())<br>

  * .equals(</tt><i>u</i><tt>)</tt>

  * </blockquote>

  *

  * if <i>u</i> is hierarchical, and

  *

  * <blockquote>

  * <tt>new URI(</tt><i>u</i><tt>.getScheme(),<br>

  * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</tt><i>u</i><tt>.getUserInfo(),&nbsp;</tt><i>u</i><tt>.getHost(),&nbsp;</tt><i>u</i><tt>.getPort(),<br>

  * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</tt><i>u</i><tt>.getPath(),&nbsp;</tt><i>u</i><tt>.getQuery(),<br>

  * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</tt><i>u</i><tt>.getFragment())<br>

  * .equals(</tt><i>u</i><tt>)</tt>

  * </blockquote>

  *

  * if <i>u</i> is hierarchical and has either no authority or a server-based

  * authority.

  *

  *

  * <h4> URIs, URLs, and URNs </h4>

  *

  * A URI is a uniform resource <i>identifier</i> while a URL is a uniform

  * resource <i>locator</i>.  Hence every URL is a URI, abstractly speaking, but

  * not every URI is a URL.  This is because there is another subcategory of

  * URIs, uniform resource <i>names</i> (URNs), which name resources but do not

  * specify how to locate them.  The <tt>mailto</tt>, <tt>news</tt>, and

  * <tt>isbn</tt> URIs shown above are examples of URNs.

  *

  * <p> The conceptual distinction between URIs and URLs is reflected in the

  * differences between this class and the {@link URL} class.

  *

  * <p> An instance of this class represents a URI reference in the syntactic

  * sense defined by RFC 2396.  A URI may be either absolute or relative.

  * A URI string is parsed according to the generic syntax without regard to the

  * scheme, if any, that it specifies.  No lookup of the host, if any, is

  * performed, and no scheme-dependent stream handler is constructed.  Equality,

  * hashing, and comparison are defined strictly in terms of the character

  * content of the instance.  In other words, a URI instance is little more than

  * a structured string that supports the syntactic, scheme-independent

  * operations of comparison, normalization, resolution, and relativization.

  *

  * <p> An instance of the {@link URL} class, by contrast, represents the

  * syntactic components of a URL together with some of the information required

  * to access the resource that it describes.  A URL must be absolute, that is,

  * it must always specify a scheme.  A URL string is parsed according to its

  * scheme.  A stream handler is always established for a URL, and in fact it is

  * impossible to create a URL instance for a scheme for which no handler is

  * available.  Equality and hashing depend upon both the scheme and the

  * Internet address of the host, if any; comparison is not defined.  In other

  * words, a URL is a structured string that supports the syntactic operation of

  * resolution as well as the network I/O operations of looking up the host and

  * opening a connection to the specified resource.

  *

  *

  * @author Mark Reinhold

  * @since 1.4

  *

  * @see <a href="http://www.ietf.org/rfc/rfc2279.txt"><i>RFC&nbsp;2279: UTF-8, a

  * transformation format of ISO 10646</i></a>, <br><a

  * href="http://www.ietf.org/rfc/rfc2373.txt"><i>RFC&nbsp;2373: IPv6 Addressing

  * Architecture</i></a>, <br><a

  * href="http://www.ietf.org/rfc/rfc2396.txt"><i>RFC&nbsp;2396: Uniform

  * Resource Identifiers (URI): Generic Syntax</i></a>, <br><a

  * href="http://www.ietf.org/rfc/rfc2732.txt"><i>RFC&nbsp;2732: Format for

  * Literal IPv6 Addresses in URLs</i></a>, <br><a

  * href="URISyntaxException.html">URISyntaxException</a>

  */

 public final class URI

     implements Comparable<URI>, Serializable

 {

     // Note: Comments containing the word "ASSERT" indicate places where a

     // throw of an InternalError should be replaced by an appropriate assertion

     // statement once asserts are enabled in the build.

     static final long serialVersionUID = -6052424284110960213L;

     // -- Properties and components of this instance --

     // Components of all URIs: [<scheme>:]<scheme-specific-part>[#<fragment>]

     private transient String scheme;            // null ==> relative URI

     private transient String fragment;

     // Hierarchical URI components: [//<authority>]<path>[?<query>]

     private transient String authority;         // Registry or server

     // Server-based authority: [<userInfo>@]<host>[:<port>]

     private transient String userInfo;

     private transient String host;              // null ==> registry-based

     private transient int port = -1;            // -1 ==> undefined

     // Remaining components of hierarchical URIs

     private transient String path;              // null ==> opaque

     private transient String query;

     // The remaining fields may be computed on demand

     private volatile transient String schemeSpecificPart;

     private volatile transient int hash;        // Zero ==> undefined

     private volatile transient String decodedUserInfo = null;

     private volatile transient String decodedAuthority = null;

     private volatile transient String decodedPath = null;

     private volatile transient String decodedQuery = null;

     private volatile transient String decodedFragment = null;

     private volatile transient String decodedSchemeSpecificPart = null;

     /**

      * The string form of this URI.

      *

      * @serial

      */

     private volatile String string;             // The only serializable field

     // -- Constructors and factories --

     private URI() { }                           // Used internally

     /**

      * Constructs a URI by parsing the given string.

      *

      * <p> This constructor parses the given string exactly as specified by the

      * grammar in <a

      * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,

      * Appendix&nbsp;A, <b><i>except for the following deviations:</i></b> </p>

      *

      * <ul type=disc>

      *

      *   <li><p> An empty authority component is permitted as long as it is

      *   followed by a non-empty path, a query component, or a fragment

      *   component.  This allows the parsing of URIs such as

      *   <tt>"file:///foo/bar"</tt>, which seems to be the intent of

      *   RFC 2396 although the grammar does not permit it.  If the

      *   authority component is empty then the user-information, host, and port

      *   components are undefined. </p></li>

      *

      *   <li><p> Empty relative paths are permitted; this seems to be the

      *   intent of RFC 2396 although the grammar does not permit it.  The

      *   primary consequence of this deviation is that a standalone fragment

      *   such as <tt>"#foo"</tt> parses as a relative URI with an empty path

      *   and the given fragment, and can be usefully <a

      *   href="#resolve-frag">resolved</a> against a base URI.

      *

      *   <li><p> IPv4 addresses in host components are parsed rigorously, as

      *   specified by <a

      *   href="http://www.ietf.org/rfc/rfc2732.txt">RFC&nbsp;2732</a>: Each

      *   element of a dotted-quad address must contain no more than three

      *   decimal digits.  Each element is further constrained to have a value

      *   no greater than 255. </p></li>

      *

      *   <li> <p> Hostnames in host components that comprise only a single

      *   domain label are permitted to start with an <i>alphanum</i>

      *   character. This seems to be the intent of <a

      *   href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>

      *   section 3.2.2 although the grammar does not permit it. The

      *   consequence of this deviation is that the authority component of a

      *   hierarchical URI such as <tt>s://123</tt>, will parse as a server-based

      *   authority. </p></li>

      *

      *   <li><p> IPv6 addresses are permitted for the host component.  An IPv6

      *   address must be enclosed in square brackets (<tt>'['</tt> and

      *   <tt>']'</tt>) as specified by <a

      *   href="http://www.ietf.org/rfc/rfc2732.txt">RFC&nbsp;2732</a>.  The

      *   IPv6 address itself must parse according to <a

      *   href="http://www.ietf.org/rfc/rfc2373.txt">RFC&nbsp;2373</a>.  IPv6

      *   addresses are further constrained to describe no more than sixteen

      *   bytes of address information, a constraint implicit in RFC 2373

      *   but not expressible in the grammar. </p></li>

      *

      *   <li><p> Characters in the <i>other</i> category are permitted wherever

      *   RFC&nbsp;2396 permits <i>escaped</i> octets, that is, in the

      *   user-information, path, query, and fragment components, as well as in

      *   the authority component if the authority is registry-based.  This

      *   allows URIs to contain Unicode characters beyond those in the US-ASCII

      *   character set. </p></li>

      *

      * </ul>

      *

      * @param  str   The string to be parsed into a URI

      *

      * @throws  NullPointerException

      *          If <tt>str</tt> is <tt>null</tt>

      *

      * @throws  URISyntaxException

      *          If the given string violates RFC 2396, as augmented

      *          by the above deviations

      */

     public URI(String str) throws URISyntaxException {

         new Parser(str).parse(false);

     }

     /**

      * Constructs a hierarchical URI from the given components.

      *

      * <p> If a scheme is given then the path, if also given, must either be

      * empty or begin with a slash character (<tt>'/'</tt>).  Otherwise a

      * component of the new URI may be left undefined by passing <tt>null</tt>

      * for the corresponding parameter or, in the case of the <tt>port</tt>

      * parameter, by passing <tt>-1</tt>.

      *

      * <p> This constructor first builds a URI string from the given components

      * according to the rules specified in <a

      * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,

      * section&nbsp;5.2, step&nbsp;7: </p>

      *

      * <ol>

      *

      *   <li><p> Initially, the result string is empty. </p></li>

      *

      *   <li><p> If a scheme is given then it is appended to the result,

      *   followed by a colon character (<tt>':'</tt>).  </p></li>

      *

      *   <li><p> If user information, a host, or a port are given then the

      *   string <tt>"//"</tt> is appended.  </p></li>

      *

      *   <li><p> If user information is given then it is appended, followed by

      *   a commercial-at character (<tt>'@'</tt>).  Any character not in the

      *   <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, or <i>other</i>

      *   categories is <a href="#quote">quoted</a>.  </p></li>

      *

      *   <li><p> If a host is given then it is appended.  If the host is a

      *   literal IPv6 address but is not enclosed in square brackets

      *   (<tt>'['</tt> and <tt>']'</tt>) then the square brackets are added.

      *   </p></li>

      *

      *   <li><p> If a port number is given then a colon character

      *   (<tt>':'</tt>) is appended, followed by the port number in decimal.

      *   </p></li>

      *

      *   <li><p> If a path is given then it is appended.  Any character not in

      *   the <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, or <i>other</i>

      *   categories, and not equal to the slash character (<tt>'/'</tt>) or the

      *   commercial-at character (<tt>'@'</tt>), is quoted.  </p></li>

      *

      *   <li><p> If a query is given then a question-mark character

      *   (<tt>'?'</tt>) is appended, followed by the query.  Any character that

      *   is not a <a href="#legal-chars">legal URI character</a> is quoted.

      *   </p></li>

      *

      *   <li><p> Finally, if a fragment is given then a hash character

      *   (<tt>'#'</tt>) is appended, followed by the fragment.  Any character

      *   that is not a legal URI character is quoted.  </p></li>

      *

      * </ol>

      *

      * <p> The resulting URI string is then parsed as if by invoking the {@link

      * #URI(String)} constructor and then invoking the {@link

      * #parseServerAuthority()} method upon the result; this may cause a {@link

      * URISyntaxException} to be thrown.  </p>

      *

      * @param   scheme    Scheme name

      * @param   userInfo  User name and authorization information

      * @param   host      Host name

      * @param   port      Port number

      * @param   path      Path

      * @param   query     Query

      * @param   fragment  Fragment

      *

      * @throws URISyntaxException

      *         If both a scheme and a path are given but the path is relative,

      *         if the URI string constructed from the given components violates

      *         RFC 2396, or if the authority component of the string is

      *         present but cannot be parsed as a server-based authority

      */

     public URI(String scheme,

                String userInfo, String host, int port,

                String path, String query, String fragment)

         throws URISyntaxException

     {

         String s = toString(scheme, null,

                             null, userInfo, host, port,

                             path, query, fragment);

         checkPath(s, scheme, path);

         new Parser(s).parse(true);

     }

     /**

      * Constructs a hierarchical URI from the given components.

      *

      * <p> If a scheme is given then the path, if also given, must either be

      * empty or begin with a slash character (<tt>'/'</tt>).  Otherwise a

      * component of the new URI may be left undefined by passing <tt>null</tt>

      * for the corresponding parameter.

      *

      * <p> This constructor first builds a URI string from the given components

      * according to the rules specified in <a

      * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,

      * section&nbsp;5.2, step&nbsp;7: </p>

      *

      * <ol>

      *

      *   <li><p> Initially, the result string is empty.  </p></li>

      *

      *   <li><p> If a scheme is given then it is appended to the result,

      *   followed by a colon character (<tt>':'</tt>).  </p></li>

      *

      *   <li><p> If an authority is given then the string <tt>"//"</tt> is

      *   appended, followed by the authority.  If the authority contains a

      *   literal IPv6 address then the address must be enclosed in square

      *   brackets (<tt>'['</tt> and <tt>']'</tt>).  Any character not in the

      *   <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, or <i>other</i>

      *   categories, and not equal to the commercial-at character

      *   (<tt>'@'</tt>), is <a href="#quote">quoted</a>.  </p></li>

      *

      *   <li><p> If a path is given then it is appended.  Any character not in

      *   the <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, or <i>other</i>

      *   categories, and not equal to the slash character (<tt>'/'</tt>) or the

      *   commercial-at character (<tt>'@'</tt>), is quoted.  </p></li>

      *

      *   <li><p> If a query is given then a question-mark character

      *   (<tt>'?'</tt>) is appended, followed by the query.  Any character that

      *   is not a <a href="#legal-chars">legal URI character</a> is quoted.

      *   </p></li>

      *

      *   <li><p> Finally, if a fragment is given then a hash character

      *   (<tt>'#'</tt>) is appended, followed by the fragment.  Any character

      *   that is not a legal URI character is quoted.  </p></li>

      *

      * </ol>

      *

      * <p> The resulting URI string is then parsed as if by invoking the {@link

      * #URI(String)} constructor and then invoking the {@link

      * #parseServerAuthority()} method upon the result; this may cause a {@link

      * URISyntaxException} to be thrown.  </p>

      *

      * @param   scheme     Scheme name

      * @param   authority  Authority

      * @param   path       Path

      * @param   query      Query

      * @param   fragment   Fragment

      *

      * @throws URISyntaxException

      *         If both a scheme and a path are given but the path is relative,

      *         if the URI string constructed from the given components violates

      *         RFC 2396, or if the authority component of the string is

      *         present but cannot be parsed as a server-based authority

      */

     public URI(String scheme,

                String authority,

                String path, String query, String fragment)

         throws URISyntaxException

     {

         String s = toString(scheme, null,

                             authority, null, null, -1,

                             path, query, fragment);

         checkPath(s, scheme, path);

         new Parser(s).parse(false);

     }

     /**

      * Constructs a hierarchical URI from the given components.

      *

      * <p> A component may be left undefined by passing <tt>null</tt>.

      *

      * <p> This convenience constructor works as if by invoking the

      * seven-argument constructor as follows:

      *

      * <blockquote><tt>

      * new {@link #URI(String, String, String, int, String, String, String)

      * URI}(scheme, null, host, -1, path, null, fragment);

      * </tt></blockquote>

      *

      * @param   scheme    Scheme name

      * @param   host      Host name

      * @param   path      Path

      * @param   fragment  Fragment

      *

      * @throws  URISyntaxException

      *          If the URI string constructed from the given components

      *          violates RFC 2396

      */

     public URI(String scheme, String host, String path, String fragment)

         throws URISyntaxException

     {

         this(scheme, null, host, -1, path, null, fragment);

     }

     /**

      * Constructs a URI from the given components.

      *

      * <p> A component may be left undefined by passing <tt>null</tt>.

      *

      * <p> This constructor first builds a URI in string form using the given

      * components as follows:  </p>

      *

      * <ol>

      *

      *   <li><p> Initially, the result string is empty.  </p></li>

      *

      *   <li><p> If a scheme is given then it is appended to the result,

      *   followed by a colon character (<tt>':'</tt>).  </p></li>

      *

      *   <li><p> If a scheme-specific part is given then it is appended.  Any

      *   character that is not a <a href="#legal-chars">legal URI character</a>

      *   is <a href="#quote">quoted</a>.  </p></li>

      *

      *   <li><p> Finally, if a fragment is given then a hash character

      *   (<tt>'#'</tt>) is appended to the string, followed by the fragment.

      *   Any character that is not a legal URI character is quoted.  </p></li>

      *

      * </ol>

      *

      * <p> The resulting URI string is then parsed in order to create the new

      * URI instance as if by invoking the {@link #URI(String)} constructor;

      * this may cause a {@link URISyntaxException} to be thrown.  </p>

      *

      * @param   scheme    Scheme name

      * @param   ssp       Scheme-specific part

      * @param   fragment  Fragment

      *

      * @throws  URISyntaxException

      *          If the URI string constructed from the given components

      *          violates RFC 2396

      */

     public URI(String scheme, String ssp, String fragment)

         throws URISyntaxException

     {

         new Parser(toString(scheme, ssp,

                             null, null, null, -1,

                             null, null, fragment))

             .parse(false);

     }

     /**

      * Creates a URI by parsing the given string.

      *

      * <p> This convenience factory method works as if by invoking the {@link

      * #URI(String)} constructor; any {@link URISyntaxException} thrown by the

      * constructor is caught and wrapped in a new {@link

      * IllegalArgumentException} object, which is then thrown.

      *

      * <p> This method is provided for use in situations where it is known that

      * the given string is a legal URI, for example for URI constants declared

      * within in a program, and so it would be considered a programming error

      * for the string not to parse as such.  The constructors, which throw

      * {@link URISyntaxException} directly, should be used situations where a

      * URI is being constructed from user input or from some other source that

      * may be prone to errors.  </p>

      *

      * @param  str   The string to be parsed into a URI

      * @return The new URI

      *

      * @throws  NullPointerException

      *          If <tt>str</tt> is <tt>null</tt>

      *

      * @throws  IllegalArgumentException

      *          If the given string violates RFC 2396

      */

     public static URI create(String str) {

         try {

             return new URI(str);

         } catch (URISyntaxException x) {

             throw new IllegalArgumentException(x.getMessage(), x);

         }

     }

     // -- Operations --

     /**

      * Attempts to parse this URI's authority component, if defined, into

      * user-information, host, and port components.

      *

      * <p> If this URI's authority component has already been recognized as

      * being server-based then it will already have been parsed into

      * user-information, host, and port components.  In this case, or if this

      * URI has no authority component, this method simply returns this URI.

      *

      * <p> Otherwise this method attempts once more to parse the authority

      * component into user-information, host, and port components, and throws

      * an exception describing why the authority component could not be parsed

      * in that way.

      *

      * <p> This method is provided because the generic URI syntax specified in

      * <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>

      * cannot always distinguish a malformed server-based authority from a

      * legitimate registry-based authority.  It must therefore treat some

      * instances of the former as instances of the latter.  The authority

      * component in the URI string <tt>"//foo:bar"</tt>, for example, is not a

      * legal server-based authority but it is legal as a registry-based

      * authority.

      *

      * <p> In many common situations, for example when working URIs that are

      * known to be either URNs or URLs, the hierarchical URIs being used will

      * always be server-based.  They therefore must either be parsed as such or

      * treated as an error.  In these cases a statement such as

      *

      * <blockquote>

      * <tt>URI </tt><i>u</i><tt> = new URI(str).parseServerAuthority();</tt>

      * </blockquote>

      *

      * <p> can be used to ensure that <i>u</i> always refers to a URI that, if

      * it has an authority component, has a server-based authority with proper

      * user-information, host, and port components.  Invoking this method also

      * ensures that if the authority could not be parsed in that way then an

      * appropriate diagnostic message can be issued based upon the exception

      * that is thrown. </p>

      *

      * @return  A URI whose authority field has been parsed

      *          as a server-based authority

      *

      * @throws  URISyntaxException

      *          If the authority component of this URI is defined

      *          but cannot be parsed as a server-based authority

      *          according to RFC 2396

      */

     public URI parseServerAuthority()

         throws URISyntaxException

     {

         // We could be clever and cache the error message and index from the

         // exception thrown during the original parse, but that would require

         // either more fields or a more-obscure representation.

         if ((host != null) || (authority == null))

             return this;

         defineString();

         new Parser(string).parse(true);

         return this;

     }

     /**

      * Normalizes this URI's path.

      *

      * <p> If this URI is opaque, or if its path is already in normal form,

      * then this URI is returned.  Otherwise a new URI is constructed that is

      * identical to this URI except that its path is computed by normalizing

      * this URI's path in a manner consistent with <a

      * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,

      * section 5.2, step 6, sub-steps c through f; that is:

      * </p>

      *

      * <ol>

      *

      *   <li><p> All <tt>"."</tt> segments are removed. </p></li>

      *

      *   <li><p> If a <tt>".."</tt> segment is preceded by a non-<tt>".."</tt>

      *   segment then both of these segments are removed.  This step is

      *   repeated until it is no longer applicable. </p></li>

      *

      *   <li><p> If the path is relative, and if its first segment contains a

      *   colon character (<tt>':'</tt>), then a <tt>"."</tt> segment is

      *   prepended.  This prevents a relative URI with a path such as

      *   <tt>"a:b/c/d"</tt> from later being re-parsed as an opaque URI with a

      *   scheme of <tt>"a"</tt> and a scheme-specific part of <tt>"b/c/d"</tt>.

      *   <b><i>(Deviation from RFC&nbsp;2396)</i></b> </p></li>

      *

      * </ol>

      *

      * <p> A normalized path will begin with one or more <tt>".."</tt> segments

      * if there were insufficient non-<tt>".."</tt> segments preceding them to

      * allow their removal.  A normalized path will begin with a <tt>"."</tt>

      * segment if one was inserted by step 3 above.  Otherwise, a normalized

      * path will not contain any <tt>"."</tt> or <tt>".."</tt> segments. </p>

      *

      * @return  A URI equivalent to this URI,

      *          but whose path is in normal form

      */

     public URI normalize() {

         return normalize(this);

     }

     /**

      * Resolves the given URI against this URI.

      *

      * <p> If the given URI is already absolute, or if this URI is opaque, then

      * the given URI is returned.

      *

      * <p><a name="resolve-frag"></a> If the given URI's fragment component is

      * defined, its path component is empty, and its scheme, authority, and

      * query components are undefined, then a URI with the given fragment but

      * with all other components equal to those of this URI is returned.  This

      * allows a URI representing a standalone fragment reference, such as

      * <tt>"#foo"</tt>, to be usefully resolved against a base URI.

      *

      * <p> Otherwise this method constructs a new hierarchical URI in a manner

      * consistent with <a

      * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,

      * section&nbsp;5.2; that is: </p>

      *

      * <ol>

      *

      *   <li><p> A new URI is constructed with this URI's scheme and the given

      *   URI's query and fragment components. </p></li>

      *

      *   <li><p> If the given URI has an authority component then the new URI's

      *   authority and path are taken from the given URI. </p></li>

      *

      *   <li><p> Otherwise the new URI's authority component is copied from

      *   this URI, and its path is computed as follows: </p>

      *

      *   <ol type=a>

      *

      *     <li><p> If the given URI's path is absolute then the new URI's path

      *     is taken from the given URI. </p></li>

      *

      *     <li><p> Otherwise the given URI's path is relative, and so the new

      *     URI's path is computed by resolving the path of the given URI

      *     against the path of this URI.  This is done by concatenating all but

      *     the last segment of this URI's path, if any, with the given URI's

      *     path and then normalizing the result as if by invoking the {@link

      *     #normalize() normalize} method. </p></li>

      *

      *   </ol></li>

      *

      * </ol>

      *

      * <p> The result of this method is absolute if, and only if, either this

      * URI is absolute or the given URI is absolute.  </p>

      *

      * @param  uri  The URI to be resolved against this URI

      * @return The resulting URI

      *

      * @throws  NullPointerException

      *          If <tt>uri</tt> is <tt>null</tt>

      */

     public URI resolve(URI uri) {

         return resolve(this, uri);

     }

     /**

      * Constructs a new URI by parsing the given string and then resolving it

      * against this URI.

      *

      * <p> This convenience method works as if invoking it were equivalent to

      * evaluating the expression <tt>{@link #resolve(java.net.URI)

      * resolve}(URI.{@link #create(String) create}(str))</tt>. </p>

      *

      * @param  str   The string to be parsed into a URI

      * @return The resulting URI

      *

      * @throws  NullPointerException

      *          If <tt>str</tt> is <tt>null</tt>

      *

      * @throws  IllegalArgumentException

      *          If the given string violates RFC 2396

      */

     public URI resolve(String str) {

         return resolve(URI.create(str));

     }

     /**

      * Relativizes the given URI against this URI.

      *

      * <p> The relativization of the given URI against this URI is computed as

      * follows: </p>

      *

      * <ol>

      *

      *   <li><p> If either this URI or the given URI are opaque, or if the

      *   scheme and authority components of the two URIs are not identical, or

      *   if the path of this URI is not a prefix of the path of the given URI,

      *   then the given URI is returned. </p></li>

      *

      *   <li><p> Otherwise a new relative hierarchical URI is constructed with

      *   query and fragment components taken from the given URI and with a path

      *   component computed by removing this URI's path from the beginning of

      *   the given URI's path. </p></li>

      *

      * </ol>

      *

      * @param  uri  The URI to be relativized against this URI

      * @return The resulting URI

      *

      * @throws  NullPointerException

      *          If <tt>uri</tt> is <tt>null</tt>

      */

     public URI relativize(URI uri) {

         return relativize(this, uri);

     }

     /**

      * Constructs a URL from this URI.

      *

      * <p> This convenience method works as if invoking it were equivalent to

      * evaluating the expression <tt>new&nbsp;URL(this.toString())</tt> after

      * first checking that this URI is absolute. </p>

      *

      * @return  A URL constructed from this URI

      *

      * @throws  IllegalArgumentException

      *          If this URL is not absolute

      *

      * @throws  MalformedURLException

      *          If a protocol handler for the URL could not be found,

      *          or if some other error occurred while constructing the URL

      */

     public URL toURL()

         throws MalformedURLException {

         if (!isAbsolute())

             throw new IllegalArgumentException("URI is not absolute");

         return new URL(toString());

     }

     // -- Component access methods --

     /**

      * Returns the scheme component of this URI.

      *

      * <p> The scheme component of a URI, if defined, only contains characters

      * in the <i>alphanum</i> category and in the string <tt>"-.+"</tt>.  A

      * scheme always starts with an <i>alpha</i> character. <p>

      *

      * The scheme component of a URI cannot contain escaped octets, hence this

      * method does not perform any decoding.

      *

      * @return  The scheme component of this URI,

      *          or <tt>null</tt> if the scheme is undefined

      */

     public String getScheme() {

         return scheme;

     }

     /**

      * Tells whether or not this URI is absolute.

      *

      * <p> A URI is absolute if, and only if, it has a scheme component. </p>

      *

      * @return  <tt>true</tt> if, and only if, this URI is absolute

      */

     public boolean isAbsolute() {

         return scheme != null;

     }

     /**

      * Tells whether or not this URI is opaque.

      *

      * <p> A URI is opaque if, and only if, it is absolute and its

      * scheme-specific part does not begin with a slash character ('/').

      * An opaque URI has a scheme, a scheme-specific part, and possibly

      * a fragment; all other components are undefined. </p>

      *

      * @return  <tt>true</tt> if, and only if, this URI is opaque

      */

     public boolean isOpaque() {

         return path == null;

     }

     /**

      * Returns the raw scheme-specific part of this URI.  The scheme-specific

      * part is never undefined, though it may be empty.

      *

      * <p> The scheme-specific part of a URI only contains legal URI

      * characters. </p>

      *

      * @return  The raw scheme-specific part of this URI

      *          (never <tt>null</tt>)

      */

     public String getRawSchemeSpecificPart() {

         defineSchemeSpecificPart();

         return schemeSpecificPart;

     }

     /**

      * Returns the decoded scheme-specific part of this URI.

      *

      * <p> The string returned by this method is equal to that returned by the

      * {@link #getRawSchemeSpecificPart() getRawSchemeSpecificPart} method

      * except that all sequences of escaped octets are <a

      * href="#decode">decoded</a>.  </p>

      *

      * @return  The decoded scheme-specific part of this URI

      *          (never <tt>null</tt>)

      */

     public String getSchemeSpecificPart() {

         if (decodedSchemeSpecificPart == null)

             decodedSchemeSpecificPart = decode(getRawSchemeSpecificPart());

         return decodedSchemeSpecificPart;

     }

     /**

      * Returns the raw authority component of this URI.

      *

      * <p> The authority component of a URI, if defined, only contains the

      * commercial-at character (<tt>'@'</tt>) and characters in the

      * <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, and <i>other</i>

      * categories.  If the authority is server-based then it is further

      * constrained to have valid user-information, host, and port

      * components. </p>

      *

      * @return  The raw authority component of this URI,

      *          or <tt>null</tt> if the authority is undefined

      */

     public String getRawAuthority() {

         return authority;

     }

     /**

      * Returns the decoded authority component of this URI.

      *

      * <p> The string returned by this method is equal to that returned by the

      * {@link #getRawAuthority() getRawAuthority} method except that all

      * sequences of escaped octets are <a href="#decode">decoded</a>.  </p>

      *

      * @return  The decoded authority component of this URI,

      *          or <tt>null</tt> if the authority is undefined

      */

     public String getAuthority() {

         if (decodedAuthority == null)

             decodedAuthority = decode(authority);

         return decodedAuthority;

     }

     /**

      * Returns the raw user-information component of this URI.

      *

      * <p> The user-information component of a URI, if defined, only contains

      * characters in the <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, and

      * <i>other</i> categories. </p>

      *

      * @return  The raw user-information component of this URI,

      *          or <tt>null</tt> if the user information is undefined

      */

     public String getRawUserInfo() {

         return userInfo;

     }

     /**

      * Returns the decoded user-information component of this URI.

      *

      * <p> The string returned by this method is equal to that returned by the

      * {@link #getRawUserInfo() getRawUserInfo} method except that all

      * sequences of escaped octets are <a href="#decode">decoded</a>.  </p>

      *

      * @return  The decoded user-information component of this URI,

      *          or <tt>null</tt> if the user information is undefined

      */

     public String getUserInfo() {

         if ((decodedUserInfo == null) && (userInfo != null))

             decodedUserInfo = decode(userInfo);

         return decodedUserInfo;

     }

     /**

      * Returns the host component of this URI.

      *

      * <p> The host component of a URI, if defined, will have one of the

      * following forms: </p>

      *

      * <ul type=disc>

      *

      *   <li><p> A domain name consisting of one or more <i>labels</i>

      *   separated by period characters (<tt>'.'</tt>), optionally followed by

      *   a period character.  Each label consists of <i>alphanum</i> characters

      *   as well as hyphen characters (<tt>'-'</tt>), though hyphens never

      *   occur as the first or last characters in a label. The rightmost

      *   label of a domain name consisting of two or more labels, begins

      *   with an <i>alpha</i> character. </li>

      *

      *   <li><p> A dotted-quad IPv4 address of the form

      *   <i>digit</i><tt>+.</tt><i>digit</i><tt>+.</tt><i>digit</i><tt>+.</tt><i>digit</i><tt>+</tt>,

      *   where no <i>digit</i> sequence is longer than three characters and no

      *   sequence has a value larger than 255. </p></li>

      *

      *   <li><p> An IPv6 address enclosed in square brackets (<tt>'['</tt> and

      *   <tt>']'</tt>) and consisting of hexadecimal digits, colon characters

      *   (<tt>':'</tt>), and possibly an embedded IPv4 address.  The full

      *   syntax of IPv6 addresses is specified in <a

      *   href="http://www.ietf.org/rfc/rfc2373.txt"><i>RFC&nbsp;2373: IPv6

      *   Addressing Architecture</i></a>.  </p></li>

      *

      * </ul>

      *

      * The host component of a URI cannot contain escaped octets, hence this

      * method does not perform any decoding.

      *

      * @return  The host component of this URI,

      *          or <tt>null</tt> if the host is undefined

      */

     public String getHost() {

         return host;

     }

     /**

      * Returns the port number of this URI.

      *

      * <p> The port component of a URI, if defined, is a non-negative

      * integer. </p>

      *

      * @return  The port component of this URI,

      *          or <tt>-1</tt> if the port is undefined

      */

     public int getPort() {

         return port;

     }

     /**

      * Returns the raw path component of this URI.

      *

      * <p> The path component of a URI, if defined, only contains the slash

      * character (<tt>'/'</tt>), the commercial-at character (<tt>'@'</tt>),

      * and characters in the <i>unreserved</i>, <i>punct</i>, <i>escaped</i>,

      * and <i>other</i> categories. </p>

      *

      * @return  The path component of this URI,

      *          or <tt>null</tt> if the path is undefined

      */

     public String getRawPath() {

         return path;

     }

     /**

      * Returns the decoded path component of this URI.

      *

      * <p> The string returned by this method is equal to that returned by the

      * {@link #getRawPath() getRawPath} method except that all sequences of

      * escaped octets are <a href="#decode">decoded</a>.  </p>

      *

      * @return  The decoded path component of this URI,

      *          or <tt>null</tt> if the path is undefined

      */

     public String getPath() {

         if ((decodedPath == null) && (path != null))

             decodedPath = decode(path);

         return decodedPath;

     }

     /**

      * Returns the raw query component of this URI.

      *

      * <p> The query component of a URI, if defined, only contains legal URI

      * characters. </p>

      *

      * @return  The raw query component of this URI,

      *          or <tt>null</tt> if the query is undefined

      */

     public String getRawQuery() {

         return query;

     }

     /**

      * Returns the decoded query component of this URI.

      *

      * <p> The string returned by this method is equal to that returned by the

      * {@link #getRawQuery() getRawQuery} method except that all sequences of

      * escaped octets are <a href="#decode">decoded</a>.  </p>

      *

      * @return  The decoded query component of this URI,

      *          or <tt>null</tt> if the query is undefined

      */

     public String getQuery() {

         if ((decodedQuery == null) && (query != null))

             decodedQuery = decode(query);

         return decodedQuery;

     }

     /**

      * Returns the raw fragment component of this URI.

      *

      * <p> The fragment component of a URI, if defined, only contains legal URI

      * characters. </p>

      *

      * @return  The raw fragment component of this URI,

      *          or <tt>null</tt> if the fragment is undefined

      */

     public String getRawFragment() {

         return fragment;

     }

     /**

      * Returns the decoded fragment component of this URI.

      *

      * <p> The string returned by this method is equal to that returned by the

      * {@link #getRawFragment() getRawFragment} method except that all

      * sequences of escaped octets are <a href="#decode">decoded</a>.  </p>

      *

      * @return  The decoded fragment component of this URI,

      *          or <tt>null</tt> if the fragment is undefined

      */

     public String getFragment() {

         if ((decodedFragment == null) && (fragment != null))

             decodedFragment = decode(fragment);

         return decodedFragment;

     }

     // -- Equality, comparison, hash code, toString, and serialization --

     /**

      * Tests this URI for equality with another object.

      *

      * <p> If the given object is not a URI then this method immediately

      * returns <tt>false</tt>.

      *

      * <p> For two URIs to be considered equal requires that either both are

      * opaque or both are hierarchical.  Their schemes must either both be

      * undefined or else be equal without regard to case. Their fragments

      * must either both be undefined or else be equal.

      *

      * <p> For two opaque URIs to be considered equal, their scheme-specific

      * parts must be equal.

      *

      * <p> For two hierarchical URIs to be considered equal, their paths must

      * be equal and their queries must either both be undefined or else be

      * equal.  Their authorities must either both be undefined, or both be

      * registry-based, or both be server-based.  If their authorities are

      * defined and are registry-based, then they must be equal.  If their

      * authorities are defined and are server-based, then their hosts must be

      * equal without regard to case, their port numbers must be equal, and

      * their user-information components must be equal.

      *

      * <p> When testing the user-information, path, query, fragment, authority,

      * or scheme-specific parts of two URIs for equality, the raw forms rather

      * than the encoded forms of these components are compared and the

      * hexadecimal digits of escaped octets are compared without regard to

      * case.

      *

      * <p> This method satisfies the general contract of the {@link

      * java.lang.Object#equals(Object) Object.equals} method. </p>

      *

      * @param   ob   The object to which this object is to be compared

      *

      * @return  <tt>true</tt> if, and only if, the given object is a URI that

      *          is identical to this URI

      */

     public boolean equals(Object ob) {

         if (ob == this)

             return true;

         if (!(ob instanceof URI))

             return false;

         URI that = (URI)ob;

         if (this.isOpaque() != that.isOpaque()) return false;

         if (!equalIgnoringCase(this.scheme, that.scheme)) return false;

         if (!equal(this.fragment, that.fragment)) return false;

         // Opaque

         if (this.isOpaque())

             return equal(this.schemeSpecificPart, that.schemeSpecificPart);

         // Hierarchical

         if (!equal(this.path, that.path)) return false;

         if (!equal(this.query, that.query)) return false;

         // Authorities

         if (this.authority == that.authority) return true;

         if (this.host != null) {

             // Server-based

             if (!equal(this.userInfo, that.userInfo)) return false;

             if (!equalIgnoringCase(this.host, that.host)) return false;

             if (this.port != that.port) return false;

         } else if (this.authority != null) {

             // Registry-based

             if (!equal(this.authority, that.authority)) return false;

         } else if (this.authority != that.authority) {

             return false;

         }

         return true;

     }

     /**

      * Returns a hash-code value for this URI.  The hash code is based upon all

      * of the URI's components, and satisfies the general contract of the

      * {@link java.lang.Object#hashCode() Object.hashCode} method.

      *

      * @return  A hash-code value for this URI

      */

     public int hashCode() {

         if (hash != 0)

             return hash;

         int h = hashIgnoringCase(0, scheme);

         h = hash(h, fragment);

         if (isOpaque()) {

             h = hash(h, schemeSpecificPart);

         } else {

             h = hash(h, path);

             h = hash(h, query);

             if (host != null) {

                 h = hash(h, userInfo);

                 h = hashIgnoringCase(h, host);

                 h += 1949 * port;

             } else {

                 h = hash(h, authority);

             }

         }

         hash = h;

         return h;

     }

     /**

      * Compares this URI to another object, which must be a URI.

      *

      * <p> When comparing corresponding components of two URIs, if one

      * component is undefined but the other is defined then the first is

      * considered to be less than the second.  Unless otherwise noted, string

      * components are ordered according to their natural, case-sensitive

      * ordering as defined by the {@link java.lang.String#compareTo(Object)

      * String.compareTo} method.  String components that are subject to

      * encoding are compared by comparing their raw forms rather than their

      * encoded forms.

      *

      * <p> The ordering of URIs is defined as follows: </p>

      *

      * <ul type=disc>

      *

      *   <li><p> Two URIs with different schemes are ordered according the

      *   ordering of their schemes, without regard to case. </p></li>

      *

      *   <li><p> A hierarchical URI is considered to be less than an opaque URI

      *   with an identical scheme. </p></li>

      *

      *   <li><p> Two opaque URIs with identical schemes are ordered according

      *   to the ordering of their scheme-specific parts. </p></li>

      *

      *   <li><p> Two opaque URIs with identical schemes and scheme-specific

      *   parts are ordered according to the ordering of their

      *   fragments. </p></li>

      *

      *   <li><p> Two hierarchical URIs with identical schemes are ordered

      *   according to the ordering of their authority components: </p>

      *

      *   <ul type=disc>

      *

      *     <li><p> If both authority components are server-based then the URIs

      *     are ordered according to their user-information components; if these

      *     components are identical then the URIs are ordered according to the

      *     ordering of their hosts, without regard to case; if the hosts are

      *     identical then the URIs are ordered according to the ordering of

      *     their ports. </p></li>

      *

      *     <li><p> If one or both authority components are registry-based then

      *     the URIs are ordered according to the ordering of their authority

      *     components. </p></li>

      *

      *   </ul></li>

      *

      *   <li><p> Finally, two hierarchical URIs with identical schemes and

      *   authority components are ordered according to the ordering of their

      *   paths; if their paths are identical then they are ordered according to

      *   the ordering of their queries; if the queries are identical then they

      *   are ordered according to the order of their fragments. </p></li>

      *

      * </ul>

      *

      * <p> This method satisfies the general contract of the {@link

      * java.lang.Comparable#compareTo(Object) Comparable.compareTo}

      * method. </p>

      *

      * @param   that

      *          The object to which this URI is to be compared

      *

      * @return  A negative integer, zero, or a positive integer as this URI is

      *          less than, equal to, or greater than the given URI

      *

      * @throws  ClassCastException

      *          If the given object is not a URI

      */

     public int compareTo(URI that) {

         int c;

         if ((c = compareIgnoringCase(this.scheme, that.scheme)) != 0)

             return c;

         if (this.isOpaque()) {

             if (that.isOpaque()) {

                 // Both opaque

                 if ((c = compare(this.schemeSpecificPart,

                                  that.schemeSpecificPart)) != 0)

                     return c;

                 return compare(this.fragment, that.fragment);

             }

             return +1;                  // Opaque > hierarchical

         } else if (that.isOpaque()) {

             return -1;                  // Hierarchical < opaque

         }

         // Hierarchical

         if ((this.host != null) && (that.host != null)) {

             // Both server-based

             if ((c = compare(this.userInfo, that.userInfo)) != 0)

                 return c;

             if ((c = compareIgnoringCase(this.host, that.host)) != 0)

                 return c;

             if ((c = this.port - that.port) != 0)

                 return c;

         } else {

             // If one or both authorities are registry-based then we simply

             // compare them in the usual, case-sensitive way.  If one is

             // registry-based and one is server-based then the strings are

             // guaranteed to be unequal, hence the comparison will never return

             // zero and the compareTo and equals methods will remain

             // consistent.

             if ((c = compare(this.authority, that.authority)) != 0) return c;

         }

         if ((c = compare(this.path, that.path)) != 0) return c;

         if ((c = compare(this.query, that.query)) != 0) return c;

         return compare(this.fragment, that.fragment);

     }

     /**

      * Returns the content of this URI as a string.

      *

      * <p> If this URI was created by invoking one of the constructors in this

      * class then a string equivalent to the original input string, or to the

      * string computed from the originally-given components, as appropriate, is

      * returned.  Otherwise this URI was created by normalization, resolution,

      * or relativization, and so a string is constructed from this URI's

      * components according to the rules specified in <a

      * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,

      * section&nbsp;5.2, step&nbsp;7. </p>

      *

      * @return  The string form of this URI

      */

     public String toString() {

         defineString();

         return string;

     }

     /**

      * Returns the content of this URI as a US-ASCII string.

      *

      * <p> If this URI does not contain any characters in the <i>other</i>

      * category then an invocation of this method will return the same value as

      * an invocation of the {@link #toString() toString} method.  Otherwise

      * this method works as if by invoking that method and then <a

      * href="#encode">encoding</a> the result.  </p>

      *

      * @return  The string form of this URI, encoded as needed

      *          so that it only contains characters in the US-ASCII

      *          charset

      */

     public String toASCIIString() {

         defineString();

         return encode(string);

     }

     // -- Serialization support --

     /**

      * Saves the content of this URI to the given serial stream.

      *

      * <p> The only serializable field of a URI instance is its <tt>string</tt>

      * field.  That field is given a value, if it does not have one already,

      * and then the {@link java.io.ObjectOutputStream#defaultWriteObject()}

      * method of the given object-output stream is invoked. </p>

      *

      * @param  os  The object-output stream to which this object

      *             is to be written

      */

     private void writeObject(ObjectOutputStream os)

         throws IOException

     {

         defineString();

         os.defaultWriteObject();        // Writes the string field only

     }

     /**

      * Reconstitutes a URI from the given serial stream.

      *

      * <p> The {@link java.io.ObjectInputStream#defaultReadObject()} method is

      * invoked to read the value of the <tt>string</tt> field.  The result is

      * then parsed in the usual way.

      *

      * @param  is  The object-input stream from which this object

      *             is being read

      */

     private void readObject(ObjectInputStream is)

         throws ClassNotFoundException, IOException

     {

         port = -1;                      // Argh

         is.defaultReadObject();

         try {

             new Parser(string).parse(false);

         } catch (URISyntaxException x) {

             IOException y = new InvalidObjectException("Invalid URI");

             y.initCause(x);

             throw y;

         }

     }

     // -- End of public methods --

     // -- Utility methods for string-field comparison and hashing --

     // These methods return appropriate values for null string arguments,

     // thereby simplifying the equals, hashCode, and compareTo methods.

     //

     // The case-ignoring methods should only be applied to strings whose

     // characters are all known to be US-ASCII.  Because of this restriction,

     // these methods are faster than the similar methods in the String class.

     // US-ASCII only

     private static int toLower(char c) {

         if ((c >= 'A') && (c <= 'Z'))

             return c + ('a' - 'A');

         return c;

     }

     private static boolean equal(String s, String t) {

         if (s == t) return true;

         if ((s != null) && (t != null)) {

             if (s.length() != t.length())

                 return false;

             if (s.indexOf('%') < 0)

                 return s.equals(t);

             int n = s.length();

             for (int i = 0; i < n;) {

                 char c = s.charAt(i);

                 char d = t.charAt(i);

                 if (c != '%') {

                     if (c != d)

                         return false;

                     i++;

                     continue;

                 }

                 i++;

                 if (toLower(s.charAt(i)) != toLower(t.charAt(i)))

                     return false;

                 i++;

                 if (toLower(s.charAt(i)) != toLower(t.charAt(i)))

                     return false;

                 i++;

             }

             return true;

         }

         return false;

     }

     // US-ASCII only

     private static boolean equalIgnoringCase(String s, String t) {

         if (s == t) return true;

         if ((s != null) && (t != null)) {

             int n = s.length();

             if (t.length() != n)

                 return false;

             for (int i = 0; i < n; i++) {

                 if (toLower(s.charAt(i)) != toLower(t.charAt(i)))

                     return false;

             }

             return true;

         }

         return false;

     }

     private static int hash(int hash, String s) {

         if (s == null) return hash;

         return hash * 127 + s.hashCode();

     }

     // US-ASCII only

     private static int hashIgnoringCase(int hash, String s) {

         if (s == null) return hash;

         int h = hash;

         int n = s.length();

         for (int i = 0; i < n; i++)

             h = 31 * h + toLower(s.charAt(i));

         return h;

     }

     private static int compare(String s, String t) {

         if (s == t) return 0;

         if (s != null) {

             if (t != null)

                 return s.compareTo(t);

             else

                 return +1;

         } else {

             return -1;

         }

     }

     // US-ASCII only

     private static int compareIgnoringCase(String s, String t) {

         if (s == t) return 0;

         if (s != null) {

             if (t != null) {

                 int sn = s.length();

                 int tn = t.length();

                 int n = sn < tn ? sn : tn;

                 for (int i = 0; i < n; i++) {

                     int c = toLower(s.charAt(i)) - toLower(t.charAt(i));

                     if (c != 0)

                         return c;

                 }

                 return sn - tn;

             }

             return +1;

         } else {

             return -1;

         }

     }

     // -- String construction --

     // If a scheme is given then the path, if given, must be absolute

     //

     private static void checkPath(String s, String scheme, String path)

         throws URISyntaxException

     {

         if (scheme != null) {

             if ((path != null)

                 && ((path.length() > 0) && (path.charAt(0) != '/')))

                 throw new URISyntaxException(s,

                                              "Relative path in absolute URI");

         }

     }

     private void appendAuthority(StringBuffer sb,

                                  String authority,

                                  String userInfo,

                                  String host,

                                  int port)

     {

         if (host != null) {

             sb.append("//");

             if (userInfo != null) {

                 sb.append(quote(userInfo, L_USERINFO, H_USERINFO));

                 sb.append('@');

             }

             boolean needBrackets = ((host.indexOf(':') >= 0)

                                     && !host.startsWith("[")

                                     && !host.endsWith("]"));

             if (needBrackets) sb.append('[');

             sb.append(host);

             if (needBrackets) sb.append(']');

             if (port != -1) {

                 sb.append(':');

                 sb.append(port);

             }

         } else if (authority != null) {

             sb.append("//");

             if (authority.startsWith("[")) {

                 // authority should (but may not) contain an embedded IPv6 address

                 int end = authority.indexOf("]");

                 String doquote = authority, dontquote = "";

                 if (end != -1 && authority.indexOf(":") != -1) {

                     // the authority contains an IPv6 address

                     if (end == authority.length()) {

                         dontquote = authority;

                         doquote = "";

                     } else {

                         dontquote = authority.substring(0 , end + 1);

                         doquote = authority.substring(end + 1);

                     }

                 }

                 sb.append(dontquote);

                 sb.append(quote(doquote,

                             L_REG_NAME | L_SERVER,

                             H_REG_NAME | H_SERVER));

             } else {

                 sb.append(quote(authority,

                             L_REG_NAME | L_SERVER,

                             H_REG_NAME | H_SERVER));

             }

         }

     }

     private void appendSchemeSpecificPart(StringBuffer sb,

                                           String opaquePart,

                                           String authority,

                                           String userInfo,

                                           String host,

                                           int port,

                                           String path,

                                           String query)

     {

         if (opaquePart != null) {

             /* check if SSP begins with an IPv6 address

              * because we must not quote a literal IPv6 address

              */

             if (opaquePart.startsWith("//[")) {

                 int end =  opaquePart.indexOf("]");

                 if (end != -1 && opaquePart.indexOf(":")!=-1) {

                     String doquote, dontquote;

                     if (end == opaquePart.length()) {

                         dontquote = opaquePart;

                         doquote = "";

                     } else {

                         dontquote = opaquePart.substring(0,end+1);

                         doquote = opaquePart.substring(end+1);

                     }

                     sb.append (dontquote);

                     sb.append(quote(doquote, L_URIC, H_URIC));

                 }

             } else {

                 sb.append(quote(opaquePart, L_URIC, H_URIC));

             }

         } else {

             appendAuthority(sb, authority, userInfo, host, port);

             if (path != null)

                 sb.append(quote(path, L_PATH, H_PATH));

             if (query != null) {

                 sb.append('?');

                 sb.append(quote(query, L_URIC, H_URIC));

             }

         }

     }

     private void appendFragment(StringBuffer sb, String fragment) {

         if (fragment != null) {

             sb.append('#');

             sb.append(quote(fragment, L_URIC, H_URIC));

         }

     }

     private String toString(String scheme,

                             String opaquePart,

                             String authority,

                             String userInfo,

                             String host,

                             int port,

                             String path,

                             String query,

                             String fragment)

     {

         StringBuffer sb = new StringBuffer();

         if (scheme != null) {

             sb.append(scheme);

             sb.append(':');

         }

         appendSchemeSpecificPart(sb, opaquePart,

                                  authority, userInfo, host, port,

                                  path, query);

         appendFragment(sb, fragment);

         return sb.toString();

     }

     private void defineSchemeSpecificPart() {

         if (schemeSpecificPart != null) return;

         StringBuffer sb = new StringBuffer();

         appendSchemeSpecificPart(sb, null, getAuthority(), getUserInfo(),

                                  host, port, getPath(), getQuery());

         if (sb.length() == 0) return;

         schemeSpecificPart = sb.toString();

     }

     private void defineString() {

         if (string != null) return;

         StringBuffer sb = new StringBuffer();

         if (scheme != null) {

             sb.append(scheme);

             sb.append(':');

         }

         if (isOpaque()) {

             sb.append(schemeSpecificPart);

         } else {

             if (host != null) {

                 sb.append("//");

                 if (userInfo != null) {

                     sb.append(userInfo);

                     sb.append('@');

                 }

                 boolean needBrackets = ((host.indexOf(':') >= 0)

                                     && !host.startsWith("[")

                                     && !host.endsWith("]"));

                 if (needBrackets) sb.append('[');

                 sb.append(host);

                 if (needBrackets) sb.append(']');

                 if (port != -1) {

                     sb.append(':');

                     sb.append(port);

                 }

             } else if (authority != null) {

                 sb.append("//");

                 sb.append(authority);

             }

             if (path != null)

                 sb.append(path);

             if (query != null) {

                 sb.append('?');

                 sb.append(query);

             }

         }

         if (fragment != null) {

             sb.append('#');

             sb.append(fragment);

         }

         string = sb.toString();

     }

     // -- Normalization, resolution, and relativization --

     // RFC2396 5.2 (6)

     private static String resolvePath(String base, String child,

                                       boolean absolute)

     {

         int i = base.lastIndexOf('/');

         int cn = child.length();

         String path = "";

         if (cn == 0) {

             // 5.2 (6a)

             if (i >= 0)

                 path = base.substring(0, i + 1);

         } else {

             StringBuffer sb = new StringBuffer(base.length() + cn);

             // 5.2 (6a)

             if (i >= 0)

                 sb.append(base.substring(0, i + 1));

             // 5.2 (6b)

             sb.append(child);

             path = sb.toString();

         }

         // 5.2 (6c-f)

         String np = normalize(path);

         // 5.2 (6g): If the result is absolute but the path begins with "../",

         // then we simply leave the path as-is

         return np;

     }

     // RFC2396 5.2

     private static URI resolve(URI base, URI child) {

         // check if child if opaque first so that NPE is thrown

         // if child is null.

         if (child.isOpaque() || base.isOpaque())

             return child;

         // 5.2 (2): Reference to current document (lone fragment)

         if ((child.scheme == null) && (child.authority == null)

             && child.path.equals("") && (child.fragment != null)

             && (child.query == null)) {

             if ((base.fragment != null)

                 && child.fragment.equals(base.fragment)) {

                 return base;

             }

             URI ru = new URI();

             ru.scheme = base.scheme;

             ru.authority = base.authority;

             ru.userInfo = base.userInfo;

             ru.host = base.host;

             ru.port = base.port;

             ru.path = base.path;

             ru.fragment = child.fragment;

             ru.query = base.query;

             return ru;

         }

         // 5.2 (3): Child is absolute

         if (child.scheme != null)

             return child;

         URI ru = new URI();             // Resolved URI

         ru.scheme = base.scheme;

         ru.query = child.query;

         ru.fragment = child.fragment;

         // 5.2 (4): Authority

         if (child.authority == null) {

             ru.authority = base.authority;

             ru.host = base.host;

             ru.userInfo = base.userInfo;

             ru.port = base.port;

             String cp = (child.path == null) ? "" : child.path;

             if ((cp.length() > 0) && (cp.charAt(0) == '/')) {

                 // 5.2 (5): Child path is absolute

                 ru.path = child.path;

             } else {

                 // 5.2 (6): Resolve relative path

                 ru.path = resolvePath(base.path, cp, base.isAbsolute());

             }

         } else {

             ru.authority = child.authority;

             ru.host = child.host;

             ru.userInfo = child.userInfo;

             ru.host = child.host;

             ru.port = child.port;

             ru.path = child.path;

         }

         // 5.2 (7): Recombine (nothing to do here)

         return ru;

     }

     // If the given URI's path is normal then return the URI;

     // o.w., return a new URI containing the normalized path.

     //

     private static URI normalize(URI u) {

         if (u.isOpaque() || (u.path == null) || (u.path.length() == 0))

             return u;

         String np = normalize(u.path);

         if (np == u.path)

             return u;

         URI v = new URI();

         v.scheme = u.scheme;

         v.fragment = u.fragment;

         v.authority = u.authority;

         v.userInfo = u.userInfo;

         v.host = u.host;

         v.port = u.port;

         v.path = np;

         v.query = u.query;

         return v;

     }

     // If both URIs are hierarchical, their scheme and authority components are

     // identical, and the base path is a prefix of the child's path, then

     // return a relative URI that, when resolved against the base, yields the

     // child; otherwise, return the child.

     //

     private static URI relativize(URI base, URI child) {

         // check if child if opaque first so that NPE is thrown

         // if child is null.

         if (child.isOpaque() || base.isOpaque())

             return child;

         if (!equalIgnoringCase(base.scheme, child.scheme)

             || !equal(base.authority, child.authority))

             return child;

         String bp = normalize(base.path);

         String cp = normalize(child.path);

         if (!bp.equals(cp)) {

             if (!bp.endsWith("/"))

                 bp = bp + "/";

             if (!cp.startsWith(bp))

                 return child;

         }

         URI v = new URI();

         v.path = cp.substring(bp.length());

         v.query = child.query;

         v.fragment = child.fragment;

         return v;

     }

     // -- Path normalization --

     // The following algorithm for path normalization avoids the creation of a

     // string object for each segment, as well as the use of a string buffer to

     // compute the final result, by using a single char array and editing it in

     // place.  The array is first split into segments, replacing each slash

     // with '\0' and creating a segment-index array, each element of which is

     // the index of the first char in the corresponding segment.  We then walk

     // through both arrays, removing ".", "..", and other segments as necessary

     // by setting their entries in the index array to -1.  Finally, the two

     // arrays are used to rejoin the segments and compute the final result.

     //

     // This code is based upon src/solaris/native/java/io/canonicalize_md.c

     // Check the given path to see if it might need normalization.  A path

     // might need normalization if it contains duplicate slashes, a "."

     // segment, or a ".." segment.  Return -1 if no further normalization is

     // possible, otherwise return the number of segments found.

     //

     // This method takes a string argument rather than a char array so that

     // this test can be performed without invoking path.toCharArray().

     //

     static private int needsNormalization(String path) {

         boolean normal = true;

         int ns = 0;                     // Number of segments

         int end = path.length() - 1;    // Index of last char in path

         int p = 0;                      // Index of next char in path

         // Skip initial slashes

         while (p <= end) {

             if (path.charAt(p) != '/') break;

             p++;

         }

         if (p > 1) normal = false;

         // Scan segments

         while (p <= end) {

             // Looking at "." or ".." ?

             if ((path.charAt(p) == '.')

                 && ((p == end)

                     || ((path.charAt(p + 1) == '/')

                         || ((path.charAt(p + 1) == '.')

                             && ((p + 1 == end)

                                 || (path.charAt(p + 2) == '/')))))) {

                 normal = false;

             }

             ns++;

             // Find beginning of next segment

             while (p <= end) {

                 if (path.charAt(p++) != '/')

                     continue;

                 // Skip redundant slashes

                 while (p <= end) {

                     if (path.charAt(p) != '/') break;

                     normal = false;

                     p++;

                 }

                 break;

             }

         }

         return normal ? -1 : ns;

     }

     // Split the given path into segments, replacing slashes with nulls and

     // filling in the given segment-index array.

     //

     // Preconditions:

     //   segs.length == Number of segments in path

     //

     // Postconditions:

     //   All slashes in path replaced by '\0'

     //   segs[i] == Index of first char in segment i (0 <= i < segs.length)

     //

     static private void split(char[] path, int[] segs) {

         int end = path.length - 1;      // Index of last char in path

         int p = 0;                      // Index of next char in path

         int i = 0;                      // Index of current segment

         // Skip initial slashes

         while (p <= end) {

             if (path[p] != '/') break;

             path[p] = '\0';

             p++;

         }

         while (p <= end) {

             // Note start of segment

             segs[i++] = p++;

             // Find beginning of next segment

             while (p <= end) {

                 if (path[p++] != '/')

                     continue;

                 path[p - 1] = '\0';

                 // Skip redundant slashes

                 while (p <= end) {

                     if (path[p] != '/') break;

                     path[p++] = '\0';

                 }

                 break;

             }

         }

         if (i != segs.length)

             throw new InternalError();  // ASSERT

     }

     // Join the segments in the given path according to the given segment-index

     // array, ignoring those segments whose index entries have been set to -1,

     // and inserting slashes as needed.  Return the length of the resulting

     // path.

     //

     // Preconditions:

     //   segs[i] == -1 implies segment i is to be ignored

     //   path computed by split, as above, with '\0' having replaced '/'

     //

     // Postconditions:

     //   path[0] .. path[return value] == Resulting path

     //

     static private int join(char[] path, int[] segs) {

         int ns = segs.length;           // Number of segments

         int end = path.length - 1;      // Index of last char in path

         int p = 0;                      // Index of next path char to write

         if (path[p] == '\0') {

             // Restore initial slash for absolute paths

             path[p++] = '/';

         }

         for (int i = 0; i < ns; i++) {

             int q = segs[i];            // Current segment

             if (q == -1)

                 // Ignore this segment

                 continue;

             if (p == q) {

                 // We're already at this segment, so just skip to its end

                 while ((p <= end) && (path[p] != '\0'))

                     p++;

                 if (p <= end) {

                     // Preserve trailing slash

                     path[p++] = '/';

                 }

             } else if (p < q) {

                 // Copy q down to p

                 while ((q <= end) && (path[q] != '\0'))

                     path[p++] = path[q++];

                 if (q <= end) {

                     // Preserve trailing slash

                     path[p++] = '/';

                 }

             } else

                 throw new InternalError(); // ASSERT false

         }

         return p;

     }

     // Remove "." segments from the given path, and remove segment pairs

     // consisting of a non-".." segment followed by a ".." segment.

     //

     private static void removeDots(char[] path, int[] segs) {

         int ns = segs.length;

         int end = path.length - 1;

         for (int i = 0; i < ns; i++) {

             int dots = 0;               // Number of dots found (0, 1, or 2)

             // Find next occurrence of "." or ".."

             do {

                 int p = segs[i];

                 if (path[p] == '.') {

                     if (p == end) {

                         dots = 1;

                         break;

                     } else if (path[p + 1] == '\0') {

                         dots = 1;

                         break;

                     } else if ((path[p + 1] == '.')

                                && ((p + 1 == end)

                                    || (path[p + 2] == '\0'))) {

                         dots = 2;

                         break;

                     }

                 }

                 i++;

             } while (i < ns);

             if ((i > ns) || (dots == 0))

                 break;

             if (dots == 1) {

                 // Remove this occurrence of "."

                 segs[i] = -1;

             } else {

                 // If there is a preceding non-".." segment, remove both that

                 // segment and this occurrence of ".."; otherwise, leave this

                 // ".." segment as-is.

                 int j;

                 for (j = i - 1; j >= 0; j--) {

                     if (segs[j] != -1) break;

                 }

                 if (j >= 0) {

                     int q = segs[j];

                     if (!((path[q] == '.')

                           && (path[q + 1] == '.')

                           && (path[q + 2] == '\0'))) {

                         segs[i] = -1;

                         segs[j] = -1;

                     }

                 }

             }

         }

     }

     // DEVIATION: If the normalized path is relative, and if the first

     // segment could be parsed as a scheme name, then prepend a "." segment

     //

     private static void maybeAddLeadingDot(char[] path, int[] segs) {

         if (path[0] == '\0')

             // The path is absolute

             return;

         int ns = segs.length;

         int f = 0;                      // Index of first segment

         while (f < ns) {

             if (segs[f] >= 0)

                 break;

             f++;

         }

         if ((f >= ns) || (f == 0))

             // The path is empty, or else the original first segment survived,

             // in which case we already know that no leading "." is needed

             return;

         int p = segs[f];

         while ((p < path.length) && (path[p] != ':') && (path[p] != '\0')) p++;

         if (p >= path.length || path[p] == '\0')

             // No colon in first segment, so no "." needed

             return;

         // At this point we know that the first segment is unused,

         // hence we can insert a "." segment at that position

         path[0] = '.';

         path[1] = '\0';

         segs[0] = 0;

     }

     // Normalize the given path string.  A normal path string has no empty

     // segments (i.e., occurrences of "//"), no segments equal to ".", and no

     // segments equal to ".." that are preceded by a segment not equal to "..".

     // In contrast to Unix-style pathname normalization, for URI paths we

     // always retain trailing slashes.

     //

     private static String normalize(String ps) {

         // Does this path need normalization?

         int ns = needsNormalization(ps);        // Number of segments

         if (ns < 0)

             // Nope -- just return it

             return ps;

         char[] path = ps.toCharArray();         // Path in char-array form

         // Split path into segments

         int[] segs = new int[ns];               // Segment-index array

         split(path, segs);

         // Remove dots

         removeDots(path, segs);

         // Prevent scheme-name confusion

         maybeAddLeadingDot(path, segs);

         // Join the remaining segments and return the result

         String s = new String(path, 0, join(path, segs));

         if (s.equals(ps)) {

             // string was already normalized

             return ps;

         }

         return s;

     }

     // -- Character classes for parsing --

     // RFC2396 precisely specifies which characters in the US-ASCII charset are

     // permissible in the various components of a URI reference.  We here

     // define a set of mask pairs to aid in enforcing these restrictions.  Each

     // mask pair consists of two longs, a low mask and a high mask.  Taken

     // together they represent a 128-bit mask, where bit i is set iff the

     // character with value i is permitted.

     //

     // This approach is more efficient than sequentially searching arrays of

     // permitted characters.  It could be made still more efficient by

     // precompiling the mask information so that a character's presence in a

     // given mask could be determined by a single table lookup.

     // Compute the low-order mask for the characters in the given string

     private static long lowMask(String chars) {

         int n = chars.length();

         long m = 0;

         for (int i = 0; i < n; i++) {

             char c = chars.charAt(i);

             if (c < 64)

                 m |= (1L << c);

         }

         return m;

     }

     // Compute the high-order mask for the characters in the given string

     private static long highMask(String chars) {

         int n = chars.length();

         long m = 0;

         for (int i = 0; i < n; i++) {

             char c = chars.charAt(i);

             if ((c >= 64) && (c < 128))

                 m |= (1L << (c - 64));

         }

         return m;

     }

     // Compute a low-order mask for the characters

     // between first and last, inclusive

     private static long lowMask(char first, char last) {

         long m = 0;

         int f = Math.max(Math.min(first, 63), 0);

         int l = Math.max(Math.min(last, 63), 0);

         for (int i = f; i <= l; i++)

             m |= 1L << i;

         return m;

     }

     // Compute a high-order mask for the characters

     // between first and last, inclusive

     private static long highMask(char first, char last) {

         long m = 0;

         int f = Math.max(Math.min(first, 127), 64) - 64;

         int l = Math.max(Math.min(last, 127), 64) - 64;

         for (int i = f; i <= l; i++)

             m |= 1L << i;

         return m;

     }

     // Tell whether the given character is permitted by the given mask pair

     private static boolean match(char c, long lowMask, long highMask) {

         if (c == 0) // 0 doesn't have a slot in the mask. So, it never matches.

             return false;

         if (c < 64)

             return ((1L << c) & lowMask) != 0;

         if (c < 128)

             return ((1L << (c - 64)) & highMask) != 0;

         return false;

     }

     // Character-class masks, in reverse order from RFC2396 because

     // initializers for static fields cannot make forward references.

     // digit    = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |

     //            "8" | "9"

     private static final long L_DIGIT = lowMask('0', '9');

     private static final long H_DIGIT = 0L;

     // upalpha  = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" |

     //            "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" |

     //            "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z"

     private static final long L_UPALPHA = 0L;

     private static final long H_UPALPHA = highMask('A', 'Z');

     // lowalpha = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" |

     //            "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" |

     //            "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z"

     private static final long L_LOWALPHA = 0L;

     private static final long H_LOWALPHA = highMask('a', 'z');

     // alpha         = lowalpha | upalpha

     private static final long L_ALPHA = L_LOWALPHA | L_UPALPHA;

     private static final long H_ALPHA = H_LOWALPHA | H_UPALPHA;

     // alphanum      = alpha | digit

     private static final long L_ALPHANUM = L_DIGIT | L_ALPHA;

     private static final long H_ALPHANUM = H_DIGIT | H_ALPHA;

     // hex           = digit | "A" | "B" | "C" | "D" | "E" | "F" |

     //                         "a" | "b" | "c" | "d" | "e" | "f"

     private static final long L_HEX = L_DIGIT;

     private static final long H_HEX = highMask('A', 'F') | highMask('a', 'f');

     // mark          = "-" | "_" | "." | "!" | "~" | "*" | "'" |

     //                 "(" | ")"

     private static final long L_MARK = lowMask("-_.!~*'()");

     private static final long H_MARK = highMask("-_.!~*'()");

     // unreserved    = alphanum | mark

     private static final long L_UNRESERVED = L_ALPHANUM | L_MARK;

     private static final long H_UNRESERVED = H_ALPHANUM | H_MARK;

     // reserved      = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+" |

     //                 "$" | "," | "[" | "]"

     // Added per RFC2732: "[", "]"

     private static final long L_RESERVED = lowMask(";/?:@&=+$,[]");

     private static final long H_RESERVED = highMask(";/?:@&=+$,[]");

     // The zero'th bit is used to indicate that escape pairs and non-US-ASCII

     // characters are allowed; this is handled by the scanEscape method below.

     private static final long L_ESCAPED = 1L;

     private static final long H_ESCAPED = 0L;

     // uric          = reserved | unreserved | escaped

     private static final long L_URIC = L_RESERVED | L_UNRESERVED | L_ESCAPED;

     private static final long H_URIC = H_RESERVED | H_UNRESERVED | H_ESCAPED;

     // pchar         = unreserved | escaped |

     //                 ":" | "@" | "&" | "=" | "+" | "$" | ","

     private static final long L_PCHAR

         = L_UNRESERVED | L_ESCAPED | lowMask(":@&=+$,");

     private static final long H_PCHAR

         = H_UNRESERVED | H_ESCAPED | highMask(":@&=+$,");

     // All valid path characters

     private static final long L_PATH = L_PCHAR | lowMask(";/");

     private static final long H_PATH = H_PCHAR | highMask(";/");

     // Dash, for use in domainlabel and toplabel

     private static final long L_DASH = lowMask("-");

     private static final long H_DASH = highMask("-");

     // Dot, for use in hostnames

     private static final long L_DOT = lowMask(".");

     private static final long H_DOT = highMask(".");

     // userinfo      = *( unreserved | escaped |

     //                    ";" | ":" | "&" | "=" | "+" | "$" | "," )

     private static final long L_USERINFO

         = L_UNRESERVED | L_ESCAPED | lowMask(";:&=+$,");

     private static final long H_USERINFO

         = H_UNRESERVED | H_ESCAPED | highMask(";:&=+$,");

     // reg_name      = 1*( unreserved | escaped | "$" | "," |

     //                     ";" | ":" | "@" | "&" | "=" | "+" )

     private static final long L_REG_NAME

         = L_UNRESERVED | L_ESCAPED | lowMask("$,;:@&=+");

     private static final long H_REG_NAME

         = H_UNRESERVED | H_ESCAPED | highMask("$,;:@&=+");

     // All valid characters for server-based authorities

     private static final long L_SERVER

         = L_USERINFO | L_ALPHANUM | L_DASH | lowMask(".:@[]");

     private static final long H_SERVER

         = H_USERINFO | H_ALPHANUM | H_DASH | highMask(".:@[]");

     // Special case of server authority that represents an IPv6 address

     // In this case, a % does not signify an escape sequence

     private static final long L_SERVER_PERCENT

         = L_SERVER | lowMask("%");

     private static final long H_SERVER_PERCENT

         = H_SERVER | highMask("%");

     private static final long L_LEFT_BRACKET = lowMask("[");

     private static final long H_LEFT_BRACKET = highMask("[");

     // scheme        = alpha *( alpha | digit | "+" | "-" | "." )

     private static final long L_SCHEME = L_ALPHA | L_DIGIT | lowMask("+-.");

     private static final long H_SCHEME = H_ALPHA | H_DIGIT | highMask("+-.");

     // uric_no_slash = unreserved | escaped | ";" | "?" | ":" | "@" |

     //                 "&" | "=" | "+" | "$" | ","

     private static final long L_URIC_NO_SLASH

         = L_UNRESERVED | L_ESCAPED | lowMask(";?:@&=+$,");

     private static final long H_URIC_NO_SLASH

         = H_UNRESERVED | H_ESCAPED | highMask(";?:@&=+$,");

     // -- Escaping and encoding --

     private final static char[] hexDigits = {

         '0', '1', '2', '3', '4', '5', '6', '7',

         '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'

     };

     private static void appendEscape(StringBuffer sb, byte b) {

         sb.append('%');

         sb.append(hexDigits[(b >> 4) & 0x0f]);

         sb.append(hexDigits[(b >> 0) & 0x0f]);

     }

     private static void appendEncoded(StringBuffer sb, char c) {

         /*

         ByteBuffer bb = null;

         try {

             bb = ThreadLocalCoders.encoderFor("UTF-8")

                 .encode(CharBuffer.wrap("" + c));

         } catch (CharacterCodingException x) {

             assert false;

         }

         while (bb.hasRemaining()) {

             int b = bb.get() & 0xff;

             if (b >= 0x80)

                 appendEscape(sb, (byte)b);

             else

                 sb.append((char)b);

         }

         */

     }

     // Quote any characters in s that are not permitted

     // by the given mask pair

     //

     private static String quote(String s, long lowMask, long highMask) {

         int n = s.length();

         StringBuffer sb = null;

         boolean allowNonASCII = ((lowMask & L_ESCAPED) != 0);

         for (int i = 0; i < s.length(); i++) {

             char c = s.charAt(i);

             if (c < '\u0080') {