/*

 * Copyright (c) 1995, 2010, Oracle and/or its affiliates. All rights reserved.

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

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * 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).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.util;

import java.io.IOException;

import java.io.PrintStream;

import java.io.PrintWriter;

import java.io.InputStream;

import java.io.OutputStream;

import java.io.Reader;

import java.io.Writer;

import java.io.OutputStreamWriter;

import java.io.BufferedWriter;

/**

 * The <code>Properties</code> class represents a persistent set of

 * properties. The <code>Properties</code> can be saved to a stream

 * or loaded from a stream. Each key and its corresponding value in

 * the property list is a string.

 * <p>

 * A property list can contain another property list as its

 * "defaults"; this second property list is searched if

 * the property key is not found in the original property list.

 * <p>

 * Because <code>Properties</code> inherits from <code>Hashtable</code>, the

 * <code>put</code> and <code>putAll</code> methods can be applied to a

 * <code>Properties</code> object.  Their use is strongly discouraged as they

 * allow the caller to insert entries whose keys or values are not

 * <code>Strings</code>.  The <code>setProperty</code> method should be used

 * instead.  If the <code>store</code> or <code>save</code> method is called

 * on a "compromised" <code>Properties</code> object that contains a

 * non-<code>String</code> key or value, the call will fail. Similarly,

 * the call to the <code>propertyNames</code> or <code>list</code> method

 * will fail if it is called on a "compromised" <code>Properties</code>

 * object that contains a non-<code>String</code> key.

 *

 * <p>

 * The {@link #load(java.io.Reader) load(Reader)} <tt>/</tt>

 * {@link #store(java.io.Writer, java.lang.String) store(Writer, String)}

 * methods load and store properties from and to a character based stream

 * in a simple line-oriented format specified below.

 *

 * The {@link #load(java.io.InputStream) load(InputStream)} <tt>/</tt>

 * {@link #store(java.io.OutputStream, java.lang.String) store(OutputStream, String)}

 * methods work the same way as the load(Reader)/store(Writer, String) pair, except

 * the input/output stream is encoded in ISO 8859-1 character encoding.

 * Characters that cannot be directly represented in this encoding can be written using

 * Unicode escapes as defined in section 3.3 of

 * <cite>The Java&trade; Language Specification</cite>;

 * only a single 'u' character is allowed in an escape

 * sequence. The native2ascii tool can be used to convert property files to and

 * from other character encodings.

 *

 * <p> The {@link #loadFromXML(InputStream)} and {@link

 * #storeToXML(OutputStream, String, String)} methods load and store properties

 * in a simple XML format.  By default the UTF-8 character encoding is used,

 * however a specific encoding may be specified if required.  An XML properties

 * document has the following DOCTYPE declaration:

 *

 * <pre>

 * <!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">

 * </pre>

 * Note that the system URI (http://java.sun.com/dtd/properties.dtd) is

 * <i>not</i> accessed when exporting or importing properties; it merely

 * serves as a string to uniquely identify the DTD, which is:

 * <pre>

 *    <?xml version="1.0" encoding="UTF-8"?>

 *

 *    <!-- DTD for properties -->

 *

 *    <!ELEMENT properties ( comment?, entry* ) >

 *

 *    <!ATTLIST properties version CDATA #FIXED "1.0">

 *

 *    <!ELEMENT comment (#PCDATA) >

 *

 *    <!ELEMENT entry (#PCDATA) >

 *

 *    <!ATTLIST entry key CDATA #REQUIRED>

 * </pre>

 *

 * <p>This class is thread-safe: multiple threads can share a single

 * <tt>Properties</tt> object without the need for external synchronization.

 *

 * @see <a href="../../../technotes/tools/solaris/native2ascii.html">native2ascii tool for Solaris</a>

 * @see <a href="../../../technotes/tools/windows/native2ascii.html">native2ascii tool for Windows</a>

 *

 * @author  Arthur van Hoff

 * @author  Michael McCloskey

 * @author  Xueming Shen

 * @since   JDK1.0

 */

public

class Properties extends Hashtable<Object,Object> {

    /**

     * use serialVersionUID from JDK 1.1.X for interoperability

     */

     private static final long serialVersionUID = 4112578634029874840L;

    /**

     * A property list that contains default values for any keys not

     * found in this property list.

     *

     * @serial

     */

    protected Properties defaults;

    /**

     * Creates an empty property list with no default values.

     */

    public Properties() {

        this(null);

    }

    /**

     * Creates an empty property list with the specified defaults.

     *

     * @param   defaults   the defaults.

     */

    public Properties(Properties defaults) {

        this.defaults = defaults;

    }

    /**

     * Calls the <tt>Hashtable</tt> method <code>put</code>. Provided for

     * parallelism with the <tt>getProperty</tt> method. Enforces use of

     * strings for property keys and values. The value returned is the

     * result of the <tt>Hashtable</tt> call to <code>put</code>.

     *

     * @param key the key to be placed into this property list.

     * @param value the value corresponding to <tt>key</tt>.

     * @return     the previous value of the specified key in this property

     *             list, or <code>null</code> if it did not have one.

     * @see #getProperty

     * @since    1.2

     */

    public synchronized Object setProperty(String key, String value) {

        return put(key, value);

    }

    /**

     * Reads a property list (key and element pairs) from the input

     * character stream in a simple line-oriented format.

     * <p>

     * Properties are processed in terms of lines. There are two

     * kinds of line, <i>natural lines</i> and <i>logical lines</i>.

     * A natural line is defined as a line of

     * characters that is terminated either by a set of line terminator

     * characters (<code>\n</code> or <code>\r</code> or <code>\r\n</code>)

     * or by the end of the stream. A natural line may be either a blank line,

     * a comment line, or hold all or some of a key-element pair. A logical

     * line holds all the data of a key-element pair, which may be spread

     * out across several adjacent natural lines by escaping

     * the line terminator sequence with a backslash character

     * <code>\</code>.  Note that a comment line cannot be extended

     * in this manner; every natural line that is a comment must have

     * its own comment indicator, as described below. Lines are read from

     * input until the end of the stream is reached.

     *

     * <p>

     * A natural line that contains only white space characters is

     * considered blank and is ignored.  A comment line has an ASCII

     * <code>'#'</code> or <code>'!'</code> as its first non-white

     * space character; comment lines are also ignored and do not

     * encode key-element information.  In addition to line

     * terminators, this format considers the characters space

     * (<code>' '</code>, <code>'&#92;u0020'</code>), tab

     * (<code>'\t'</code>, <code>'&#92;u0009'</code>), and form feed

     * (<code>'\f'</code>, <code>'&#92;u000C'</code>) to be white

     * space.

     *

     * <p>

     * If a logical line is spread across several natural lines, the

     * backslash escaping the line terminator sequence, the line

     * terminator sequence, and any white space at the start of the

     * following line have no affect on the key or element values.

     * The remainder of the discussion of key and element parsing

     * (when loading) will assume all the characters constituting

     * the key and element appear on a single natural line after

     * line continuation characters have been removed.  Note that

     * it is <i>not</i> sufficient to only examine the character

     * preceding a line terminator sequence to decide if the line

     * terminator is escaped; there must be an odd number of

     * contiguous backslashes for the line terminator to be escaped.

     * Since the input is processed from left to right, a

     * non-zero even number of 2<i>n</i> contiguous backslashes

     * before a line terminator (or elsewhere) encodes <i>n</i>

     * backslashes after escape processing.

     *

     * <p>

     * The key contains all of the characters in the line starting

     * with the first non-white space character and up to, but not

     * including, the first unescaped <code>'='</code>,

     * <code>':'</code>, or white space character other than a line

     * terminator. All of these key termination characters may be

     * included in the key by escaping them with a preceding backslash

     * character; for example,<p>

     *

     * <code>\:\=</code><p>

     *

     * would be the two-character key <code>":="</code>.  Line

     * terminator characters can be included using <code>\r</code> and

     * <code>\n</code> escape sequences.  Any white space after the

     * key is skipped; if the first non-white space character after

     * the key is <code>'='</code> or <code>':'</code>, then it is

     * ignored and any white space characters after it are also

     * skipped.  All remaining characters on the line become part of

     * the associated element string; if there are no remaining

     * characters, the element is the empty string

     * <code>&quot;&quot;</code>.  Once the raw character sequences

     * constituting the key and element are identified, escape

     * processing is performed as described above.

     *

     * <p>

     * As an example, each of the following three lines specifies the key

     * <code>"Truth"</code> and the associated element value

     * <code>"Beauty"</code>:

     * <p>

     * <pre>

     * Truth = Beauty

     *  Truth:Beauty

     * Truth                    :Beauty

     * </pre>

     * As another example, the following three lines specify a single

     * property:

     * <p>

     * <pre>

     * fruits                           apple, banana, pear, \

     *                                  cantaloupe, watermelon, \

     *                                  kiwi, mango

     * </pre>

     * The key is <code>"fruits"</code> and the associated element is:

     * <p>

     * <pre>"apple, banana, pear, cantaloupe, watermelon, kiwi, mango"</pre>

     * Note that a space appears before each <code>\</code> so that a space

     * will appear after each comma in the final result; the <code>\</code>,

     * line terminator, and leading white space on the continuation line are

     * merely discarded and are <i>not</i> replaced by one or more other

     * characters.

     * <p>

     * As a third example, the line:

     * <p>

     * <pre>cheeses

     * </pre>

     * specifies that the key is <code>"cheeses"</code> and the associated

     * element is the empty string <code>""</code>.<p>

     * <p>

     *

     * <a name="unicodeescapes"></a>

     * Characters in keys and elements can be represented in escape

     * sequences similar to those used for character and string literals

     * (see sections 3.3 and 3.10.6 of

     * <cite>The Java&trade; Language Specification</cite>).

     *

     * The differences from the character escape sequences and Unicode

     * escapes used for characters and strings are:

     *

     * <ul>

     * <li> Octal escapes are not recognized.

     *

     * <li> The character sequence <code>\b</code> does <i>not</i>

     * represent a backspace character.

     *

     * <li> The method does not treat a backslash character,

     * <code>\</code>, before a non-valid escape character as an

     * error; the backslash is silently dropped.  For example, in a

     * Java string the sequence <code>"\z"</code> would cause a

     * compile time error.  In contrast, this method silently drops

     * the backslash.  Therefore, this method treats the two character

     * sequence <code>"\b"</code> as equivalent to the single

     * character <code>'b'</code>.

     *

     * <li> Escapes are not necessary for single and double quotes;

     * however, by the rule above, single and double quote characters

     * preceded by a backslash still yield single and double quote

     * characters, respectively.

     *

     * <li> Only a single 'u' character is allowed in a Uniocde escape

     * sequence.

     *

     * </ul>

     * <p>

     * The specified stream remains open after this method returns.

     *

     * @param   reader   the input character stream.

     * @throws  IOException  if an error occurred when reading from the

     *          input stream.

     * @throws  IllegalArgumentException if a malformed Unicode escape

     *          appears in the input.

     * @since   1.6

     */

    public synchronized void load(Reader reader) throws IOException {

        load0(new LineReader(reader));

    }

    /**

     * Reads a property list (key and element pairs) from the input

     * byte stream. The input stream is in a simple line-oriented

     * format as specified in

     * {@link #load(java.io.Reader) load(Reader)} and is assumed to use

     * the ISO 8859-1 character encoding; that is each byte is one Latin1

     * character. Characters not in Latin1, and certain special characters,

     * are represented in keys and elements using Unicode escapes as defined in

     * section 3.3 of

     * <cite>The Java&trade; Language Specification</cite>.

     * <p>

     * The specified stream remains open after this method returns.

     *

     * @param      inStream   the input stream.

     * @exception  IOException  if an error occurred when reading from the

     *             input stream.

     * @throws     IllegalArgumentException if the input stream contains a

     *             malformed Unicode escape sequence.

     * @since 1.2

     */

    public synchronized void load(InputStream inStream) throws IOException {

        load0(new LineReader(inStream));

    }

    private void load0 (LineReader lr) throws IOException {

        char[] convtBuf = new char[1024];

        int limit;

        int keyLen;

        int valueStart;

        char c;

        boolean hasSep;

        boolean precedingBackslash;

        while ((limit = lr.readLine()) >= 0) {

            c = 0;

            keyLen = 0;

            valueStart = limit;

            hasSep = false;

            //System.out.println("line=<" + new String(lineBuf, 0, limit) + ">");

            precedingBackslash = false;

            while (keyLen < limit) {

                c = lr.lineBuf[keyLen];

                //need check if escaped.

                if ((c == '=' ||  c == ':') && !precedingBackslash) {

                    valueStart = keyLen + 1;

                    hasSep = true;

                    break;

                } else if ((c == ' ' || c == '\t' ||  c == '\f') && !precedingBackslash) {

                    valueStart = keyLen + 1;

                    break;

                }

                if (c == '\\') {

                    precedingBackslash = !precedingBackslash;

                } else {

                    precedingBackslash = false;

                }

                keyLen++;

            }

            while (valueStart < limit) {

                c = lr.lineBuf[valueStart];

                if (c != ' ' && c != '\t' &&  c != '\f') {

                    if (!hasSep && (c == '=' ||  c == ':')) {

                        hasSep = true;

                    } else {

                        break;

                    }

                }

                valueStart++;

            }

            String key = loadConvert(lr.lineBuf, 0, keyLen, convtBuf);

            String value = loadConvert(lr.lineBuf, valueStart, limit - valueStart, convtBuf);

            put(key, value);

        }

    }

    /* Read in a "logical line" from an InputStream/Reader, skip all comment

     * and blank lines and filter out those leading whitespace characters

     * (\u0020, \u0009 and \u000c) from the beginning of a "natural line".

     * Method returns the char length of the "logical line" and stores

     * the line in "lineBuf".

     */

    class LineReader {

        public LineReader(InputStream inStream) {

            this.inStream = inStream;

            inByteBuf = new byte[8192];

        }

        public LineReader(Reader reader) {

            this.reader = reader;

            inCharBuf = new char[8192];

        }

        byte[] inByteBuf;

        char[] inCharBuf;

        char[] lineBuf = new char[1024];

        int inLimit = 0;

        int inOff = 0;

        InputStream inStream;

        Reader reader;

        int readLine() throws IOException {

            int len = 0;

            char c = 0;

            boolean skipWhiteSpace = true;

            boolean isCommentLine = false;

            boolean isNewLine = true;

            boolean appendedLineBegin = false;

            boolean precedingBackslash = false;

            boolean skipLF = false;

            while (true) {

                if (inOff >= inLimit) {

                    inLimit = (inStream==null)?reader.read(inCharBuf)

                                              :inStream.read(inByteBuf);

                    inOff = 0;

                    if (inLimit <= 0) {

                        if (len == 0 || isCommentLine) {

                            return -1;

                        }

                        return len;

                    }

                }

                if (inStream != null) {

                    //The line below is equivalent to calling a

                    //ISO8859-1 decoder.

                    c = (char) (0xff & inByteBuf[inOff++]);

                } else {

                    c = inCharBuf[inOff++];

                }

                if (skipLF) {

                    skipLF = false;

                    if (c == '\n') {

                        continue;

                    }

                }

                if (skipWhiteSpace) {

                    if (c == ' ' || c == '\t' || c == '\f') {

                        continue;

                    }

                    if (!appendedLineBegin && (c == '\r' || c == '\n')) {

                        continue;

                    }

                    skipWhiteSpace = false;

                    appendedLineBegin = false;

                }

                if (isNewLine) {

                    isNewLine = false;

                    if (c == '#' || c == '!') {

                        isCommentLine = true;

                        continue;

                    }

                }

                if (c != '\n' && c != '\r') {

                    lineBuf[len++] = c;

                    if (len == lineBuf.length) {

                        int newLength = lineBuf.length * 2;

                        if (newLength < 0) {

                            newLength = Integer.MAX_VALUE;

                        }

                        char[] buf = new char[newLength];

                        System.arraycopy(lineBuf, 0, buf, 0, lineBuf.length);

                        lineBuf = buf;

                    }

                    //flip the preceding backslash flag

                    if (c == '\\') {

                        precedingBackslash = !precedingBackslash;

                    } else {

                        precedingBackslash = false;

                    }

                }

                else {

                    // reached EOL

                    if (isCommentLine || len == 0) {

                        isCommentLine = false;

                        isNewLine = true;

                        skipWhiteSpace = true;

                        len = 0;

                        continue;

                    }

                    if (inOff >= inLimit) {

                        inLimit = (inStream==null)

                                  ?reader.read(inCharBuf)

                                  :inStream.read(inByteBuf);

                        inOff = 0;

                        if (inLimit <= 0) {

                            return len;

                        }

                    }

                    if (precedingBackslash) {

                        len -= 1;

                        //skip the leading whitespace characters in following line

                        skipWhiteSpace = true;

                        appendedLineBegin = true;

                        precedingBackslash = false;

                        if (c == '\r') {

                            skipLF = true;

                        }

                    } else {

                        return len;

                    }

                }

            }

        }

    }

    /*

     * Converts encoded \uxxxx to unicode chars

     * and changes special saved chars to their original forms

     */

    private String loadConvert (char[] in, int off, int len, char[] convtBuf) {

        if (convtBuf.length < len) {

            int newLen = len * 2;

            if (newLen < 0) {

                newLen = Integer.MAX_VALUE;

            }

            convtBuf = new char[newLen];

        }

        char aChar;

        char[] out = convtBuf;

        int outLen = 0;

        int end = off + len;

        while (off < end) {

            aChar = in[off++];

            if (aChar == '\\') {

                aChar = in[off++];

                if(aChar == 'u') {

                    // Read the xxxx

                    int value=0;

                    for (int i=0; i<4; i++) {

                        aChar = in[off++];

                        switch (aChar) {

                          case '0': case '1': case '2': case '3': case '4':

                          case '5': case '6': case '7': case '8': case '9':

                             value = (value << 4) + aChar - '0';

                             break;

                          case 'a': case 'b': case 'c':

                          case 'd': case 'e': case 'f':

                             value = (value << 4) + 10 + aChar - 'a';

                             break;

                          case 'A': case 'B': case 'C':

                          case 'D': case 'E': case 'F':

                             value = (value << 4) + 10 + aChar - 'A';

                             break;

                          default:

                              throw new IllegalArgumentException(

                                           "Malformed \\uxxxx encoding.");

                        }

                     }

                    out[outLen++] = (char)value;

                } else {

                    if (aChar == 't') aChar = '\t';

                    else if (aChar == 'r') aChar = '\r';

                    else if (aChar == 'n') aChar = '\n';

                    else if (aChar == 'f') aChar = '\f';

                    out[outLen++] = aChar;

                }

            } else {

                out[outLen++] = aChar;

            }

        }

        return new String (out, 0, outLen);

    }

    /*

     * Converts unicodes to encoded \uxxxx and escapes

     * special characters with a preceding slash

     */

    private String saveConvert(String theString,

                               boolean escapeSpace,

                               boolean escapeUnicode) {

        int len = theString.length();

        int bufLen = len * 2;

        if (bufLen < 0) {

            bufLen = Integer.MAX_VALUE;

        }

        StringBuffer outBuffer = new StringBuffer(bufLen);

        for(int x=0; x<len; x++) {

            char aChar = theString.charAt(x);

            // Handle common case first, selecting largest block that

            // avoids the specials below

            if ((aChar > 61) && (aChar < 127)) {

                if (aChar == '\\') {

                    outBuffer.append('\\'); outBuffer.append('\\');

                    continue;

                }

                outBuffer.append(aChar);

                continue;

            }

            switch(aChar) {

                case ' ':

                    if (x == 0 || escapeSpace)

                        outBuffer.append('\\');

                    outBuffer.append(' ');

                    break;

                case '\t':outBuffer.append('\\'); outBuffer.append('t');

                          break;

                case '\n':outBuffer.append('\\'); outBuffer.append('n');

                          break;

                case '\r':outBuffer.append('\\'); outBuffer.append('r');

                          break;

                case '\f':outBuffer.append('\\'); outBuffer.append('f');

                          break;

                case '=': // Fall through

                case ':': // Fall through

                case '#': // Fall through

                case '!':

                    outBuffer.append('\\'); outBuffer.append(aChar);

                    break;

                default:

                    if (((aChar < 0x0020) || (aChar > 0x007e)) & escapeUnicode ) {

                        outBuffer.append('\\');

                        outBuffer.append('u');

                        outBuffer.append(toHex((aChar >> 12) & 0xF));

                        outBuffer.append(toHex((aChar >>  8) & 0xF));

                        outBuffer.append(toHex((aChar >>  4) & 0xF));

                        outBuffer.append(toHex( aChar        & 0xF));

                    } else {

                        outBuffer.append(aChar);

                    }

            }

        }

        return outBuffer.toString();

    }

    private static void writeComments(BufferedWriter bw, String comments)

        throws IOException {

        bw.write("#");

        int len = comments.length();

        int current = 0;

        int last = 0;

        char[] uu = new char[6];

        uu[0] = '\\';

        uu[1] = 'u';

        while (current < len) {

            char c = comments.charAt(current);

            if (c > '\u00ff' || c == '\n' || c == '\r') {

                if (last != current)

                    bw.write(comments.substring(last, current));

                if (c > '\u00ff') {

                    uu[2] = toHex((c >> 12) & 0xf);

                    uu[3] = toHex((c >>  8) & 0xf);

                    uu[4] = toHex((c >>  4) & 0xf);

                    uu[5] = toHex( c        & 0xf);

                    bw.write(new String(uu));

                } else {

                    bw.newLine();

                    if (c == '\r' &&

                        current != len - 1 &&

                        comments.charAt(current + 1) == '\n') {

                        current++;

                    }

                    if (current == len - 1 ||

                        (comments.charAt(current + 1) != '#' &&

                        comments.charAt(current + 1) != '!'))

                        bw.write("#");

                }

                last = current + 1;

            }

            current++;

        }

        if (last != current)

            bw.write(comments.substring(last, current));

        bw.newLine();

    }

    /**

     * Calls the <code>store(OutputStream out, String comments)</code> method

     * and suppresses IOExceptions that were thrown.

     *

     * @deprecated This method does not throw an IOException if an I/O error

     * occurs while saving the property list.  The preferred way to save a

     * properties list is via the <code>store(OutputStream out,

     * String comments)</code> method or the

     * <code>storeToXML(OutputStream os, String comment)</code> method.

     *

     * @param   out      an output stream.

     * @param   comments   a description of the property list.

     * @exception  ClassCastException  if this <code>Properties</code> object

     *             contains any keys or values that are not

     *             <code>Strings</code>.

     */

    @Deprecated

    public void save(OutputStream out, String comments)  {

        try {

            store(out, comments);

        } catch (IOException e) {

        }

    }

    /**

     * Writes this property list (key and element pairs) in this

     * <code>Properties</code> table to the output character stream in a

     * format suitable for using the {@link #load(java.io.Reader) load(Reader)}

     * method.

     * <p>

     * Properties from the defaults table of this <code>Properties</code>

     * table (if any) are <i>not</i> written out by this method.

     * <p>

     * If the comments argument is not null, then an ASCII <code>#</code>

     * character, the comments string, and a line separator are first written

     * to the output stream. Thus, the <code>comments</code> can serve as an

     * identifying comment. Any one of a line feed ('\n'), a carriage

     * return ('\r'), or a carriage return followed immediately by a line feed

     * in comments is replaced by a line separator generated by the <code>Writer</code>

     * and if the next character in comments is not character <code>#</code> or

     * character <code>!</code> then an ASCII <code>#</code> is written out

     * after that line separator.

     * <p>

     * Next, a comment line is always written, consisting of an ASCII

     * <code>#</code> character, the current date and time (as if produced

     * by the <code>toString</code> method of <code>Date</code> for the

     * current time), and a line separator as generated by the <code>Writer</code>.

     * <p>

     * Then every entry in this <code>Properties</code> table is

     * written out, one per line. For each entry the key string is

     * written, then an ASCII <code>=</code>, then the associated

     * element string. For the key, all space characters are

     * written with a preceding <code>\</code> character.  For the

     * element, leading space characters, but not embedded or trailing

     * space characters, are written with a preceding <code>\</code>

     * character. The key and element characters <code>#</code>,

     * <code>!</code>, <code>=</code>, and <code>:</code> are written

     * with a preceding backslash to ensure that they are properly loaded.

     * <p>

     * After the entries have been written, the output stream is flushed.

     * The output stream remains open after this method returns.

     * <p>

     *

     * @param   writer      an output character stream writer.

     * @param   comments   a description of the property list.

     * @exception  IOException if writing this property list to the specified

     *             output stream throws an <tt>IOException</tt>.

     * @exception  ClassCastException  if this <code>Properties</code> object

     *             contains any keys or values that are not <code>Strings</code>.

     * @exception  NullPointerException  if <code>writer</code> is null.

     * @since 1.6

     */

    public void store(Writer writer, String comments)

        throws IOException

    {

        store0((writer instanceof BufferedWriter)?(BufferedWriter)writer

                                                 : new BufferedWriter(writer),

               comments,

               false);

    }

    /**

     * Writes this property list (key and element pairs) in this

     * <code>Properties</code> table to the output stream in a format suitable

     * for loading into a <code>Properties</code> table using the

     * {@link #load(InputStream) load(InputStream)} method.

     * <p>

     * Properties from the defaults table of this <code>Properties</code>

     * table (if any) are <i>not</i> written out by this method.

     * <p>

     * This method outputs the comments, properties keys and values in

     * the same format as specified in

     * {@link #store(java.io.Writer, java.lang.String) store(Writer)},

     * with the following differences:

     * <ul>

     * <li>The stream is written using the ISO 8859-1 character encoding.

     *

     * <li>Characters not in Latin-1 in the comments are written as

     * <code>&#92;u</code><i>xxxx</i> for their appropriate unicode

     * hexadecimal value <i>xxxx</i>.

     *

     * <li>Characters less than <code>&#92;u0020</code> and characters greater

     * than <code>&#92;u007E</code> in property keys or values are written

     * as <code>&#92;u</code><i>xxxx</i> for the appropriate hexadecimal

     * value <i>xxxx</i>.

     * </ul>

     * <p>

     * After the entries have been written, the output stream is flushed.

     * The output stream remains open after this method returns.

     * <p>

     * @param   out      an output stream.

     * @param   comments   a description of the property list.

     * @exception  IOException if writing this property list to the specified

     *             output stream throws an <tt>IOException</tt>.

     * @exception  ClassCastException  if this <code>Properties</code> object

     *             contains any keys or values that are not <code>Strings</code>.

     * @exception  NullPointerException  if <code>out</code> is null.

     * @since 1.2

     */

    public void store(OutputStream out, String comments)

        throws IOException

    {

        store0(new BufferedWriter(new OutputStreamWriter(out, "8859_1")),

               comments,

               true);

    }

    private void store0(BufferedWriter bw, String comments, boolean escUnicode)

        throws IOException

    {

        if (comments != null) {

            writeComments(bw, comments);

        }

        bw.write("#" + new Date().toString());

        bw.newLine();

        synchronized (this) {

            for (Enumeration e = keys(); e.hasMoreElements();) {

                String key = (String)e.nextElement();

                String val = (String)get(key);

                key = saveConvert(key, true, escUnicode);

                /* No need to escape embedded and trailing spaces for value, hence

                 * pass false to flag.

                 */

                val = saveConvert(val, false, escUnicode);

                bw.write(key + "=" + val);

                bw.newLine();

            }

        }

        bw.flush();

    }

    /**

     * Loads all of the properties represented by the XML document on the

     * specified input stream into this properties table.

     *

     * <p>The XML document must have the following DOCTYPE declaration:

     * <pre>

     * <!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">

     * </pre>

     * Furthermore, the document must satisfy the properties DTD described

     * above.

     *

     * <p>The specified stream is closed after this method returns.

     *

     * @param in the input stream from which to read the XML document.

     * @throws IOException if reading from the specified input stream

     *         results in an <tt>IOException</tt>.

     * @throws InvalidPropertiesFormatException Data on input stream does not

     *         constitute a valid XML document with the mandated document type.

     * @throws NullPointerException if <code>in</code> is null.

     * @see    #storeToXML(OutputStream, String, String)

     * @since 1.5

     */

    public synchronized void loadFromXML(InputStream in)

        throws IOException

    {

        if (in == null)

            throw new NullPointerException();

        throw new IOException();

    }

    /**

     * Emits an XML document representing all of the properties contained

     * in this table.

     *

     * <p> An invocation of this method of the form <tt>props.storeToXML(os,

     * comment)</tt> behaves in exactly the same way as the invocation

     * <tt>props.storeToXML(os, comment, "UTF-8");</tt>.

     *

     * @param os the output stream on which to emit the XML document.

     * @param comment a description of the property list, or <code>null</code>

     *        if no comment is desired.

     * @throws IOException if writing to the specified output stream

     *         results in an <tt>IOException</tt>.

     * @throws NullPointerException if <code>os</code> is null.

     * @throws ClassCastException  if this <code>Properties</code> object

     *         contains any keys or values that are not

     *         <code>Strings</code>.

     * @see    #loadFromXML(InputStream)

     * @since 1.5

     */

    public void storeToXML(OutputStream os, String comment)

        throws IOException

    {

        if (os == null)

            throw new NullPointerException();

        storeToXML(os, comment, "UTF-8");

    }

    /**

     * Emits an XML document representing all of the properties contained

     * in this table, using the specified encoding.

     *

     * <p>The XML document will have the following DOCTYPE declaration:

     * <pre>

     * <!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">

     * </pre>

     *

     *<p>If the specified comment is <code>null</code> then no comment

     * will be stored in the document.

     *

     * <p>The specified stream remains open after this method returns.

     *

     * @param os        the output stream on which to emit the XML document.

     * @param comment   a description of the property list, or <code>null</code>

     *                  if no comment is desired.

     * @param  encoding the name of a supported

     *                  <a href="../lang/package-summary.html#charenc">

     *                  character encoding</a>

     *

     * @throws IOException if writing to the specified output stream

     *         results in an <tt>IOException</tt>.

     * @throws NullPointerException if <code>os</code> is <code>null</code>,

     *         or if <code>encoding</code> is <code>null</code>.

     * @throws ClassCastException  if this <code>Properties</code> object

     *         contains any keys or values that are not

     *         <code>Strings</code>.

     * @see    #loadFromXML(InputStream)

     * @since 1.5

     */

    public void storeToXML(OutputStream os, String comment, String encoding)

        throws IOException

    {

        if (os == null)

            throw new NullPointerException();

        throw new IOException();

    }

    /**

     * Searches for the property with the specified key in this property list.

     * If the key is not found in this property list, the default property list,

     * and its defaults, recursively, are then checked. The method returns

     * <code>null</code> if the property is not found.

     *

     * @param   key   the property key.

     * @return  the value in this property list with the specified key value.

     * @see     #setProperty

     * @see     #defaults

     */

    public String getProperty(String key) {

        Object oval = super.get(key);

        String sval = (oval instanceof String) ? (String)oval : null;

        return ((sval == null) && (defaults != null)) ? defaults.getProperty(key) : sval;

    }

    /**

     * Searches for the property with the specified key in this property list.

     * If the key is not found in this property list, the default property list,

     * and its defaults, recursively, are then checked. The method returns the

     * default value argument if the property is not found.

     *

     * @param   key            the hashtable key.

     * @param   defaultValue   a default value.

     *

     * @return  the value in this property list with the specified key value.

     * @see     #setProperty

     * @see     #defaults

     */

    public String getProperty(String key, String defaultValue) {

        String val = getProperty(key);

        return (val == null) ? defaultValue : val;

    }

    /**

     * Returns an enumeration of all the keys in this property list,

     * including distinct keys in the default property list if a key

     * of the same name has not already been found from the main

     * properties list.

     *

     * @return  an enumeration of all the keys in this property list, including

     *          the keys in the default property list.

     * @throws  ClassCastException if any key in this property list

     *          is not a string.

     * @see     java.util.Enumeration

     * @see     java.util.Properties#defaults

     * @see     #stringPropertyNames

     */

    public Enumeration<?> propertyNames() {

        Hashtable h = new Hashtable();

        enumerate(h);

        return h.keys();

    }

    /**

     * Returns a set of keys in this property list where