/*

  * Copyright (c) 1994, 2011, 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.lang;

 import java.io.*;

 import java.util.Properties;

 import java.util.PropertyPermission;

 import java.util.StringTokenizer;

 import java.security.AccessController;

 import java.security.PrivilegedAction;

 import java.security.AllPermission;

 import java.nio.channels.Channel;

 import java.nio.channels.spi.SelectorProvider;

 import sun.nio.ch.Interruptible;

 import sun.reflect.Reflection;

 import sun.security.util.SecurityConstants;

 import sun.reflect.annotation.AnnotationType;

 /**

  * The <code>System</code> class contains several useful class fields

  * and methods. It cannot be instantiated.

  *

  * <p>Among the facilities provided by the <code>System</code> class

  * are standard input, standard output, and error output streams;

  * access to externally defined properties and environment

  * variables; a means of loading files and libraries; and a utility

  * method for quickly copying a portion of an array.

  *

  * @author  unascribed

  * @since   JDK1.0

  */

 public final class System {

     /* register the natives via the static initializer.

      *

      * VM will invoke the initializeSystemClass method to complete

      * the initialization for this class separated from clinit.

      * Note that to use properties set by the VM, see the constraints

      * described in the initializeSystemClass method.

      */

     private static native void registerNatives();

     static {

         registerNatives();

     }

     /** Don't let anyone instantiate this class */

     private System() {

     }

     /**

      * The "standard" input stream. This stream is already

      * open and ready to supply input data. Typically this stream

      * corresponds to keyboard input or another input source specified by

      * the host environment or user.

      */

     public final static InputStream in = null;

     /**

      * The "standard" output stream. This stream is already

      * open and ready to accept output data. Typically this stream

      * corresponds to display output or another output destination

      * specified by the host environment or user.

      * <p>

      * For simple stand-alone Java applications, a typical way to write

      * a line of output data is:

      * <blockquote><pre>

      *     System.out.println(data)

      * </pre></blockquote>

      * <p>

      * See the <code>println</code> methods in class <code>PrintStream</code>.

      *

      * @see     java.io.PrintStream#println()

      * @see     java.io.PrintStream#println(boolean)

      * @see     java.io.PrintStream#println(char)

      * @see     java.io.PrintStream#println(char[])

      * @see     java.io.PrintStream#println(double)

      * @see     java.io.PrintStream#println(float)

      * @see     java.io.PrintStream#println(int)

      * @see     java.io.PrintStream#println(long)

      * @see     java.io.PrintStream#println(java.lang.Object)

      * @see     java.io.PrintStream#println(java.lang.String)

      */

     public final static PrintStream out = null;

     /**

      * The "standard" error output stream. This stream is already

      * open and ready to accept output data.

      * <p>

      * Typically this stream corresponds to display output or another

      * output destination specified by the host environment or user. By

      * convention, this output stream is used to display error messages

      * or other information that should come to the immediate attention

      * of a user even if the principal output stream, the value of the

      * variable <code>out</code>, has been redirected to a file or other

      * destination that is typically not continuously monitored.

      */

     public final static PrintStream err = null;

     /* The security manager for the system.

      */

     private static volatile SecurityManager security = null;

     /**

      * Reassigns the "standard" input stream.

      *

      * <p>First, if there is a security manager, its <code>checkPermission</code>

      * method is called with a <code>RuntimePermission("setIO")</code> permission

      *  to see if it's ok to reassign the "standard" input stream.

      * <p>

      *

      * @param in the new standard input stream.

      *

      * @throws SecurityException

      *        if a security manager exists and its

      *        <code>checkPermission</code> method doesn't allow

      *        reassigning of the standard input stream.

      *

      * @see SecurityManager#checkPermission

      * @see java.lang.RuntimePermission

      *

      * @since   JDK1.1

      */

     public static void setIn(InputStream in) {

         checkIO();

         setIn0(in);

     }

     /**

      * Reassigns the "standard" output stream.

      *

      * <p>First, if there is a security manager, its <code>checkPermission</code>

      * method is called with a <code>RuntimePermission("setIO")</code> permission

      *  to see if it's ok to reassign the "standard" output stream.

      *

      * @param out the new standard output stream

      *

      * @throws SecurityException

      *        if a security manager exists and its

      *        <code>checkPermission</code> method doesn't allow

      *        reassigning of the standard output stream.

      *

      * @see SecurityManager#checkPermission

      * @see java.lang.RuntimePermission

      *

      * @since   JDK1.1

      */

     public static void setOut(PrintStream out) {

         checkIO();

         setOut0(out);

     }

     /**

      * Reassigns the "standard" error output stream.

      *

      * <p>First, if there is a security manager, its <code>checkPermission</code>

      * method is called with a <code>RuntimePermission("setIO")</code> permission

      *  to see if it's ok to reassign the "standard" error output stream.

      *

      * @param err the new standard error output stream.

      *

      * @throws SecurityException

      *        if a security manager exists and its

      *        <code>checkPermission</code> method doesn't allow

      *        reassigning of the standard error output stream.

      *

      * @see SecurityManager#checkPermission

      * @see java.lang.RuntimePermission

      *

      * @since   JDK1.1

      */

     public static void setErr(PrintStream err) {

         checkIO();

         setErr0(err);

     }

     private static volatile Console cons = null;

     /**

      * Returns the unique {@link java.io.Console Console} object associated

      * with the current Java virtual machine, if any.

      *

      * @return  The system console, if any, otherwise <tt>null</tt>.

      *

      * @since   1.6

      */

      public static Console console() {

          if (cons == null) {

              synchronized (System.class) {

                  cons = sun.misc.SharedSecrets.getJavaIOAccess().console();

              }

          }

          return cons;

      }

     /**

      * Returns the channel inherited from the entity that created this

      * Java virtual machine.

      *

      * <p> This method returns the channel obtained by invoking the

      * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel

      * inheritedChannel} method of the system-wide default

      * {@link java.nio.channels.spi.SelectorProvider} object. </p>

      *

      * <p> In addition to the network-oriented channels described in

      * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel

      * inheritedChannel}, this method may return other kinds of

      * channels in the future.

      *

      * @return  The inherited channel, if any, otherwise <tt>null</tt>.

      *

      * @throws  IOException

      *          If an I/O error occurs

      *

      * @throws  SecurityException

      *          If a security manager is present and it does not

      *          permit access to the channel.

      *

      * @since 1.5

      */

     public static Channel inheritedChannel() throws IOException {

         return SelectorProvider.provider().inheritedChannel();

     }

     private static void checkIO() {

         SecurityManager sm = getSecurityManager();

         if (sm != null) {

             sm.checkPermission(new RuntimePermission("setIO"));

         }

     }

     private static native void setIn0(InputStream in);

     private static native void setOut0(PrintStream out);

     private static native void setErr0(PrintStream err);

     /**

      * Sets the System security.

      *

      * <p> If there is a security manager already installed, this method first

      * calls the security manager's <code>checkPermission</code> method

      * with a <code>RuntimePermission("setSecurityManager")</code>

      * permission to ensure it's ok to replace the existing

      * security manager.

      * This may result in throwing a <code>SecurityException</code>.

      *

      * <p> Otherwise, the argument is established as the current

      * security manager. If the argument is <code>null</code> and no

      * security manager has been established, then no action is taken and

      * the method simply returns.

      *

      * @param      s   the security manager.

      * @exception  SecurityException  if the security manager has already

      *             been set and its <code>checkPermission</code> method

      *             doesn't allow it to be replaced.

      * @see #getSecurityManager

      * @see SecurityManager#checkPermission

      * @see java.lang.RuntimePermission

      */

     public static

     void setSecurityManager(final SecurityManager s) {

         try {

             s.checkPackageAccess("java.lang");

         } catch (Exception e) {

             // no-op

         }

         setSecurityManager0(s);

     }

     private static synchronized

     void setSecurityManager0(final SecurityManager s) {

         SecurityManager sm = getSecurityManager();

         if (sm != null) {

             // ask the currently installed security manager if we

             // can replace it.

             sm.checkPermission(new RuntimePermission

                                      ("setSecurityManager"));

         }

         if ((s != null) && (s.getClass().getClassLoader() != null)) {

             // New security manager class is not on bootstrap classpath.

             // Cause policy to get initialized before we install the new

             // security manager, in order to prevent infinite loops when

             // trying to initialize the policy (which usually involves

             // accessing some security and/or system properties, which in turn

             // calls the installed security manager's checkPermission method

             // which will loop infinitely if there is a non-system class

             // (in this case: the new security manager class) on the stack).

             AccessController.doPrivileged(new PrivilegedAction<Object>() {

                 public Object run() {

                     s.getClass().getProtectionDomain().implies

                         (SecurityConstants.ALL_PERMISSION);

                     return null;

                 }

             });

         }

         security = s;

     }

     /**

      * Gets the system security interface.

      *

      * @return  if a security manager has already been established for the

      *          current application, then that security manager is returned;

      *          otherwise, <code>null</code> is returned.

      * @see     #setSecurityManager

      */

     public static SecurityManager getSecurityManager() {

         return security;

     }

     /**

      * Returns the current time in milliseconds.  Note that

      * while the unit of time of the return value is a millisecond,

      * the granularity of the value depends on the underlying

      * operating system and may be larger.  For example, many

      * operating systems measure time in units of tens of

      * milliseconds.

      *

      * <p> See the description of the class <code>Date</code> for

      * a discussion of slight discrepancies that may arise between

      * "computer time" and coordinated universal time (UTC).

      *

      * @return  the difference, measured in milliseconds, between

      *          the current time and midnight, January 1, 1970 UTC.

      * @see     java.util.Date

      */

     public static native long currentTimeMillis();

     /**

      * Returns the current value of the running Java Virtual Machine's

      * high-resolution time source, in nanoseconds.

      *

      * <p>This method can only be used to measure elapsed time and is

      * not related to any other notion of system or wall-clock time.

      * The value returned represents nanoseconds since some fixed but

      * arbitrary <i>origin</i> time (perhaps in the future, so values

      * may be negative).  The same origin is used by all invocations of

      * this method in an instance of a Java virtual machine; other

      * virtual machine instances are likely to use a different origin.

      *

      * <p>This method provides nanosecond precision, but not necessarily

      * nanosecond resolution (that is, how frequently the value changes)

      * - no guarantees are made except that the resolution is at least as

      * good as that of {@link #currentTimeMillis()}.

      *

      * <p>Differences in successive calls that span greater than

      * approximately 292 years (2<sup>63</sup> nanoseconds) will not

      * correctly compute elapsed time due to numerical overflow.

      *

      * <p>The values returned by this method become meaningful only when

      * the difference between two such values, obtained within the same

      * instance of a Java virtual machine, is computed.

      *

      * <p> For example, to measure how long some code takes to execute:

      *  <pre> {@code

      * long startTime = System.nanoTime();

      * // ... the code being measured ...

      * long estimatedTime = System.nanoTime() - startTime;}</pre>

      *

      * <p>To compare two nanoTime values

      *  <pre> {@code

      * long t0 = System.nanoTime();

      * ...

      * long t1 = System.nanoTime();}</pre>

      *

      * one should use {@code t1 - t0 < 0}, not {@code t1 < t0},

      * because of the possibility of numerical overflow.

      *

      * @return the current value of the running Java Virtual Machine's

      *         high-resolution time source, in nanoseconds

      * @since 1.5

      */

     public static native long nanoTime();

     /**

      * Copies an array from the specified source array, beginning at the

      * specified position, to the specified position of the destination array.

      * A subsequence of array components are copied from the source

      * array referenced by <code>src</code> to the destination array

      * referenced by <code>dest</code>. The number of components copied is

      * equal to the <code>length</code> argument. The components at

      * positions <code>srcPos</code> through

      * <code>srcPos+length-1</code> in the source array are copied into

      * positions <code>destPos</code> through

      * <code>destPos+length-1</code>, respectively, of the destination

      * array.

      * <p>

      * If the <code>src</code> and <code>dest</code> arguments refer to the

      * same array object, then the copying is performed as if the

      * components at positions <code>srcPos</code> through

      * <code>srcPos+length-1</code> were first copied to a temporary

      * array with <code>length</code> components and then the contents of

      * the temporary array were copied into positions

      * <code>destPos</code> through <code>destPos+length-1</code> of the

      * destination array.

      * <p>

      * If <code>dest</code> is <code>null</code>, then a

      * <code>NullPointerException</code> is thrown.

      * <p>

      * If <code>src</code> is <code>null</code>, then a

      * <code>NullPointerException</code> is thrown and the destination

      * array is not modified.

      * <p>

      * Otherwise, if any of the following is true, an

      * <code>ArrayStoreException</code> is thrown and the destination is

      * not modified:

      * <ul>

      * <li>The <code>src</code> argument refers to an object that is not an

      *     array.

      * <li>The <code>dest</code> argument refers to an object that is not an

      *     array.

      * <li>The <code>src</code> argument and <code>dest</code> argument refer

      *     to arrays whose component types are different primitive types.

      * <li>The <code>src</code> argument refers to an array with a primitive

      *    component type and the <code>dest</code> argument refers to an array

      *     with a reference component type.

      * <li>The <code>src</code> argument refers to an array with a reference

      *    component type and the <code>dest</code> argument refers to an array

      *     with a primitive component type.

      * </ul>

      * <p>

      * Otherwise, if any of the following is true, an

      * <code>IndexOutOfBoundsException</code> is

      * thrown and the destination is not modified:

      * <ul>

      * <li>The <code>srcPos</code> argument is negative.

      * <li>The <code>destPos</code> argument is negative.

      * <li>The <code>length</code> argument is negative.

      * <li><code>srcPos+length</code> is greater than

      *     <code>src.length</code>, the length of the source array.

      * <li><code>destPos+length</code> is greater than

      *     <code>dest.length</code>, the length of the destination array.

      * </ul>

      * <p>

      * Otherwise, if any actual component of the source array from

      * position <code>srcPos</code> through

      * <code>srcPos+length-1</code> cannot be converted to the component

      * type of the destination array by assignment conversion, an

      * <code>ArrayStoreException</code> is thrown. In this case, let

      * <b><i>k</i></b> be the smallest nonnegative integer less than

      * length such that <code>src[srcPos+</code><i>k</i><code>]</code>

      * cannot be converted to the component type of the destination

      * array; when the exception is thrown, source array components from

      * positions <code>srcPos</code> through

      * <code>srcPos+</code><i>k</i><code>-1</code>

      * will already have been copied to destination array positions

      * <code>destPos</code> through

      * <code>destPos+</code><i>k</I><code>-1</code> and no other

      * positions of the destination array will have been modified.

      * (Because of the restrictions already itemized, this

      * paragraph effectively applies only to the situation where both

      * arrays have component types that are reference types.)

      *

      * @param      src      the source array.

      * @param      srcPos   starting position in the source array.

      * @param      dest     the destination array.

      * @param      destPos  starting position in the destination data.

      * @param      length   the number of array elements to be copied.

      * @exception  IndexOutOfBoundsException  if copying would cause

      *               access of data outside array bounds.

      * @exception  ArrayStoreException  if an element in the <code>src</code>

      *               array could not be stored into the <code>dest</code> array

      *               because of a type mismatch.

      * @exception  NullPointerException if either <code>src</code> or

      *               <code>dest</code> is <code>null</code>.

      */

     public static native void arraycopy(Object src,  int  srcPos,

                                         Object dest, int destPos,

                                         int length);

     /**

      * Returns the same hash code for the given object as

      * would be returned by the default method hashCode(),

      * whether or not the given object's class overrides

      * hashCode().

      * The hash code for the null reference is zero.

      *

      * @param x object for which the hashCode is to be calculated

      * @return  the hashCode

      * @since   JDK1.1

      */

     public static native int identityHashCode(Object x);

     /**

      * System properties. The following properties are guaranteed to be defined:

      * <dl>

      * <dt>java.version         <dd>Java version number

      * <dt>java.vendor          <dd>Java vendor specific string

      * <dt>java.vendor.url      <dd>Java vendor URL

      * <dt>java.home            <dd>Java installation directory

      * <dt>java.class.version   <dd>Java class version number

      * <dt>java.class.path      <dd>Java classpath

      * <dt>os.name              <dd>Operating System Name

      * <dt>os.arch              <dd>Operating System Architecture

      * <dt>os.version           <dd>Operating System Version

      * <dt>file.separator       <dd>File separator ("/" on Unix)

      * <dt>path.separator       <dd>Path separator (":" on Unix)

      * <dt>line.separator       <dd>Line separator ("\n" on Unix)

      * <dt>user.name            <dd>User account name

      * <dt>user.home            <dd>User home directory

      * <dt>user.dir             <dd>User's current working directory

      * </dl>

      */

     private static Properties props;

     private static native Properties initProperties(Properties props);

     /**

      * Determines the current system properties.

      * <p>

      * First, if there is a security manager, its

      * <code>checkPropertiesAccess</code> method is called with no

      * arguments. This may result in a security exception.

      * <p>

      * The current set of system properties for use by the

      * {@link #getProperty(String)} method is returned as a

      * <code>Properties</code> object. If there is no current set of

      * system properties, a set of system properties is first created and

      * initialized. This set of system properties always includes values

      * for the following keys:

      * <table summary="Shows property keys and associated values">

      * <tr><th>Key</th>

      *     <th>Description of Associated Value</th></tr>

      * <tr><td><code>java.version</code></td>

      *     <td>Java Runtime Environment version</td></tr>

      * <tr><td><code>java.vendor</code></td>

      *     <td>Java Runtime Environment vendor</td></tr

      * <tr><td><code>java.vendor.url</code></td>

      *     <td>Java vendor URL</td></tr>

      * <tr><td><code>java.home</code></td>

      *     <td>Java installation directory</td></tr>

      * <tr><td><code>java.vm.specification.version</code></td>

      *     <td>Java Virtual Machine specification version</td></tr>

      * <tr><td><code>java.vm.specification.vendor</code></td>

      *     <td>Java Virtual Machine specification vendor</td></tr>

      * <tr><td><code>java.vm.specification.name</code></td>

      *     <td>Java Virtual Machine specification name</td></tr>

      * <tr><td><code>java.vm.version</code></td>

      *     <td>Java Virtual Machine implementation version</td></tr>

      * <tr><td><code>java.vm.vendor</code></td>

      *     <td>Java Virtual Machine implementation vendor</td></tr>

      * <tr><td><code>java.vm.name</code></td>

      *     <td>Java Virtual Machine implementation name</td></tr>

      * <tr><td><code>java.specification.version</code></td>

      *     <td>Java Runtime Environment specification  version</td></tr>

      * <tr><td><code>java.specification.vendor</code></td>

      *     <td>Java Runtime Environment specification  vendor</td></tr>

      * <tr><td><code>java.specification.name</code></td>

      *     <td>Java Runtime Environment specification  name</td></tr>

      * <tr><td><code>java.class.version</code></td>

      *     <td>Java class format version number</td></tr>

      * <tr><td><code>java.class.path</code></td>

      *     <td>Java class path</td></tr>

      * <tr><td><code>java.library.path</code></td>

      *     <td>List of paths to search when loading libraries</td></tr>

      * <tr><td><code>java.io.tmpdir</code></td>

      *     <td>Default temp file path</td></tr>

      * <tr><td><code>java.compiler</code></td>

      *     <td>Name of JIT compiler to use</td></tr>

      * <tr><td><code>java.ext.dirs</code></td>

      *     <td>Path of extension directory or directories</td></tr>

      * <tr><td><code>os.name</code></td>

      *     <td>Operating system name</td></tr>

      * <tr><td><code>os.arch</code></td>

      *     <td>Operating system architecture</td></tr>

      * <tr><td><code>os.version</code></td>

      *     <td>Operating system version</td></tr>

      * <tr><td><code>file.separator</code></td>

      *     <td>File separator ("/" on UNIX)</td></tr>

      * <tr><td><code>path.separator</code></td>

      *     <td>Path separator (":" on UNIX)</td></tr>

      * <tr><td><code>line.separator</code></td>

      *     <td>Line separator ("\n" on UNIX)</td></tr>

      * <tr><td><code>user.name</code></td>

      *     <td>User's account name</td></tr>

      * <tr><td><code>user.home</code></td>

      *     <td>User's home directory</td></tr>

      * <tr><td><code>user.dir</code></td>

      *     <td>User's current working directory</td></tr>

      * </table>

      * <p>

      * Multiple paths in a system property value are separated by the path

      * separator character of the platform.

      * <p>

      * Note that even if the security manager does not permit the

      * <code>getProperties</code> operation, it may choose to permit the

      * {@link #getProperty(String)} operation.

      *

      * @return     the system properties

      * @exception  SecurityException  if a security manager exists and its

      *             <code>checkPropertiesAccess</code> method doesn't allow access

      *              to the system properties.

      * @see        #setProperties

      * @see        java.lang.SecurityException

      * @see        java.lang.SecurityManager#checkPropertiesAccess()

      * @see        java.util.Properties

      */

     public static Properties getProperties() {

         SecurityManager sm = getSecurityManager();

         if (sm != null) {

             sm.checkPropertiesAccess();

         }

         return props;

     }

     /**

      * Returns the system-dependent line separator string.  It always

      * returns the same value - the initial value of the {@linkplain

      * #getProperty(String) system property} {@code line.separator}.

      *

      * <p>On UNIX systems, it returns {@code "\n"}; on Microsoft

      * Windows systems it returns {@code "\r\n"}.

      */

     public static String lineSeparator() {

         return lineSeparator;

     }

     private static String lineSeparator;

     /**

      * Sets the system properties to the <code>Properties</code>

      * argument.

      * <p>

      * First, if there is a security manager, its

      * <code>checkPropertiesAccess</code> method is called with no

      * arguments. This may result in a security exception.

      * <p>

      * The argument becomes the current set of system properties for use

      * by the {@link #getProperty(String)} method. If the argument is

      * <code>null</code>, then the current set of system properties is

      * forgotten.

      *

      * @param      props   the new system properties.

      * @exception  SecurityException  if a security manager exists and its

      *             <code>checkPropertiesAccess</code> method doesn't allow access

      *              to the system properties.

      * @see        #getProperties

      * @see        java.util.Properties

      * @see        java.lang.SecurityException

      * @see        java.lang.SecurityManager#checkPropertiesAccess()

      */

     public static void setProperties(Properties props) {

         SecurityManager sm = getSecurityManager();

         if (sm != null) {

             sm.checkPropertiesAccess();

         }

         if (props == null) {

             props = new Properties();

             initProperties(props);

         }

         System.props = props;

     }

     /**

      * Gets the system property indicated by the specified key.

      * <p>

      * First, if there is a security manager, its

      * <code>checkPropertyAccess</code> method is called with the key as

      * its argument. This may result in a SecurityException.

      * <p>

      * If there is no current set of system properties, a set of system

      * properties is first created and initialized in the same manner as

      * for the <code>getProperties</code> method.

      *

      * @param      key   the name of the system property.

      * @return     the string value of the system property,

      *             or <code>null</code> if there is no property with that key.

      *

      * @exception  SecurityException  if a security manager exists and its

      *             <code>checkPropertyAccess</code> method doesn't allow

      *              access to the specified system property.

      * @exception  NullPointerException if <code>key</code> is

      *             <code>null</code>.

      * @exception  IllegalArgumentException if <code>key</code> is empty.

      * @see        #setProperty

      * @see        java.lang.SecurityException

      * @see        java.lang.SecurityManager#checkPropertyAccess(java.lang.String)

      * @see        java.lang.System#getProperties()

      */

     public static String getProperty(String key) {

         checkKey(key);

         SecurityManager sm = getSecurityManager();

         if (sm != null) {

             sm.checkPropertyAccess(key);

         }

         return props.getProperty(key);

     }

     /**

      * Gets the system property indicated by the specified key.

      * <p>

      * First, if there is a security manager, its

      * <code>checkPropertyAccess</code> method is called with the

      * <code>key</code> as its argument.

      * <p>

      * If there is no current set of system properties, a set of system

      * properties is first created and initialized in the same manner as

      * for the <code>getProperties</code> method.

      *

      * @param      key   the name of the system property.

      * @param      def   a default value.

      * @return     the string value of the system property,

      *             or the default value if there is no property with that key.

      *

      * @exception  SecurityException  if a security manager exists and its

      *             <code>checkPropertyAccess</code> method doesn't allow

      *             access to the specified system property.

      * @exception  NullPointerException if <code>key</code> is

      *             <code>null</code>.

      * @exception  IllegalArgumentException if <code>key</code> is empty.

      * @see        #setProperty

      * @see        java.lang.SecurityManager#checkPropertyAccess(java.lang.String)

      * @see        java.lang.System#getProperties()

      */

     public static String getProperty(String key, String def) {

         checkKey(key);

         SecurityManager sm = getSecurityManager();

         if (sm != null) {

             sm.checkPropertyAccess(key);

         }

         return props.getProperty(key, def);

     }

     /**

      * Sets the system property indicated by the specified key.

      * <p>

      * First, if a security manager exists, its

      * <code>SecurityManager.checkPermission</code> method

      * is called with a <code>PropertyPermission(key, "write")</code>

      * permission. This may result in a SecurityException being thrown.

      * If no exception is thrown, the specified property is set to the given

      * value.

      * <p>

      *

      * @param      key   the name of the system property.

      * @param      value the value of the system property.

      * @return     the previous value of the system property,

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

      *

      * @exception  SecurityException  if a security manager exists and its

      *             <code>checkPermission</code> method doesn't allow

      *             setting of the specified property.

      * @exception  NullPointerException if <code>key</code> or

      *             <code>value</code> is <code>null</code>.

      * @exception  IllegalArgumentException if <code>key</code> is empty.

      * @see        #getProperty

      * @see        java.lang.System#getProperty(java.lang.String)

      * @see        java.lang.System#getProperty(java.lang.String, java.lang.String)

      * @see        java.util.PropertyPermission

      * @see        SecurityManager#checkPermission

      * @since      1.2

      */

     public static String setProperty(String key, String value) {

         checkKey(key);

         SecurityManager sm = getSecurityManager();

         if (sm != null) {

             sm.checkPermission(new PropertyPermission(key,

                 SecurityConstants.PROPERTY_WRITE_ACTION));

         }

         return (String) props.setProperty(key, value);

     }

     /**

      * Removes the system property indicated by the specified key.

      * <p>

      * First, if a security manager exists, its

      * <code>SecurityManager.checkPermission</code> method

      * is called with a <code>PropertyPermission(key, "write")</code>

      * permission. This may result in a SecurityException being thrown.

      * If no exception is thrown, the specified property is removed.

      * <p>

      *

      * @param      key   the name of the system property to be removed.

      * @return     the previous string value of the system property,

      *             or <code>null</code> if there was no property with that key.

      *

      * @exception  SecurityException  if a security manager exists and its

      *             <code>checkPropertyAccess</code> method doesn't allow

      *              access to the specified system property.

      * @exception  NullPointerException if <code>key</code> is

      *             <code>null</code>.

      * @exception  IllegalArgumentException if <code>key</code> is empty.

      * @see        #getProperty

      * @see        #setProperty

      * @see        java.util.Properties

      * @see        java.lang.SecurityException

      * @see        java.lang.SecurityManager#checkPropertiesAccess()

      * @since 1.5

      */

     public static String clearProperty(String key) {

         checkKey(key);

         SecurityManager sm = getSecurityManager();

         if (sm != null) {

             sm.checkPermission(new PropertyPermission(key, "write"));

         }

         return (String) props.remove(key);

     }

     private static void checkKey(String key) {

         if (key == null) {

             throw new NullPointerException("key can't be null");

         }

         if (key.equals("")) {

             throw new IllegalArgumentException("key can't be empty");

         }

     }

     /**

      * Gets the value of the specified environment variable. An

      * environment variable is a system-dependent external named

      * value.

      *

      * <p>If a security manager exists, its

      * {@link SecurityManager#checkPermission checkPermission}

      * method is called with a

      * <code>{@link RuntimePermission}("getenv."+name)</code>

      * permission.  This may result in a {@link SecurityException}

      * being thrown.  If no exception is thrown the value of the

      * variable <code>name</code> is returned.

      *

      * <p><a name="EnvironmentVSSystemProperties"><i>System

      * properties</i> and <i>environment variables</i></a> are both

      * conceptually mappings between names and values.  Both

      * mechanisms can be used to pass user-defined information to a

      * Java process.  Environment variables have a more global effect,

      * because they are visible to all descendants of the process

      * which defines them, not just the immediate Java subprocess.

      * They can have subtly different semantics, such as case

      * insensitivity, on different operating systems.  For these

      * reasons, environment variables are more likely to have

      * unintended side effects.  It is best to use system properties

      * where possible.  Environment variables should be used when a

      * global effect is desired, or when an external system interface

      * requires an environment variable (such as <code>PATH</code>).

      *

      * <p>On UNIX systems the alphabetic case of <code>name</code> is

      * typically significant, while on Microsoft Windows systems it is

      * typically not.  For example, the expression

      * <code>System.getenv("FOO").equals(System.getenv("foo"))</code>

      * is likely to be true on Microsoft Windows.

      *

      * @param  name the name of the environment variable

      * @return the string value of the variable, or <code>null</code>

      *         if the variable is not defined in the system environment

      * @throws NullPointerException if <code>name</code> is <code>null</code>

      * @throws SecurityException

      *         if a security manager exists and its

      *         {@link SecurityManager#checkPermission checkPermission}

      *         method doesn't allow access to the environment variable

      *         <code>name</code>

      * @see    #getenv()

      * @see    ProcessBuilder#environment()

      */

     public static String getenv(String name) {

         SecurityManager sm = getSecurityManager();

         if (sm != null) {

             sm.checkPermission(new RuntimePermission("getenv."+name));

         }

         return ProcessEnvironment.getenv(name);

     }

     /**

      * Returns an unmodifiable string map view of the current system environment.

      * The environment is a system-dependent mapping from names to

      * values which is passed from parent to child processes.

      *

      * <p>If the system does not support environment variables, an

      * empty map is returned.

      *

      * <p>The returned map will never contain null keys or values.

      * Attempting to query the presence of a null key or value will

      * throw a {@link NullPointerException}.  Attempting to query

      * the presence of a key or value which is not of type

      * {@link String} will throw a {@link ClassCastException}.

      *

      * <p>The returned map and its collection views may not obey the

      * general contract of the {@link Object#equals} and

      * {@link Object#hashCode} methods.

      *

      * <p>The returned map is typically case-sensitive on all platforms.

      *

      * <p>If a security manager exists, its

      * {@link SecurityManager#checkPermission checkPermission}

      * method is called with a

      * <code>{@link RuntimePermission}("getenv.*")</code>

      * permission.  This may result in a {@link SecurityException} being

      * thrown.

      *

      * <p>When passing information to a Java subprocess,

      * <a href=#EnvironmentVSSystemProperties>system properties</a>

      * are generally preferred over environment variables.

      *

      * @return the environment as a map of variable names to values

      * @throws SecurityException

      *         if a security manager exists and its

      *         {@link SecurityManager#checkPermission checkPermission}

      *         method doesn't allow access to the process environment

      * @see    #getenv(String)

      * @see    ProcessBuilder#environment()

      * @since  1.5

      */

     public static java.util.Map<String,String> getenv() {

         SecurityManager sm = getSecurityManager();

         if (sm != null) {

             sm.checkPermission(new RuntimePermission("getenv.*"));

         }

         return ProcessEnvironment.getenv();

     }

     /**

      * Terminates the currently running Java Virtual Machine. The

      * argument serves as a status code; by convention, a nonzero status

      * code indicates abnormal termination.

      * <p>

      * This method calls the <code>exit</code> method in class

      * <code>Runtime</code>. This method never returns normally.

      * <p>

      * The call <code>System.exit(n)</code> is effectively equivalent to

      * the call:

      * <blockquote><pre>

      * Runtime.getRuntime().exit(n)

      * </pre></blockquote>

      *

      * @param      status   exit status.

      * @throws  SecurityException

      *        if a security manager exists and its <code>checkExit</code>

      *        method doesn't allow exit with the specified status.

      * @see        java.lang.Runtime#exit(int)

      */

     public static void exit(int status) {

         Runtime.getRuntime().exit(status);

     }

     /**

      * Runs the garbage collector.

      * <p>

      * Calling the <code>gc</code> method suggests that the Java Virtual

      * Machine expend effort toward recycling unused objects in order to

      * make the memory they currently occupy available for quick reuse.

      * When control returns from the method call, the Java Virtual

      * Machine has made a best effort to reclaim space from all discarded

      * objects.

      * <p>

      * The call <code>System.gc()</code> is effectively equivalent to the

      * call:

      * <blockquote><pre>

      * Runtime.getRuntime().gc()

      * </pre></blockquote>

      *

      * @see     java.lang.Runtime#gc()

      */

     public static void gc() {

         Runtime.getRuntime().gc();

     }

     /**

      * Runs the finalization methods of any objects pending finalization.

      * <p>

      * Calling this method suggests that the Java Virtual Machine expend

      * effort toward running the <code>finalize</code> methods of objects

      * that have been found to be discarded but whose <code>finalize</code>

      * methods have not yet been run. When control returns from the

      * method call, the Java Virtual Machine has made a best effort to

      * complete all outstanding finalizations.

      * <p>

      * The call <code>System.runFinalization()</code> is effectively

      * equivalent to the call:

      * <blockquote><pre>

      * Runtime.getRuntime().runFinalization()

      * </pre></blockquote>

      *

      * @see     java.lang.Runtime#runFinalization()

      */

     public static void runFinalization() {

         Runtime.getRuntime().runFinalization();

     }

     /**

      * Enable or disable finalization on exit; doing so specifies that the

      * finalizers of all objects that have finalizers that have not yet been

      * automatically invoked are to be run before the Java runtime exits.

      * By default, finalization on exit is disabled.

      *

      * <p>If there is a security manager,

      * its <code>checkExit</code> method is first called

      * with 0 as its argument to ensure the exit is allowed.

      * This could result in a SecurityException.

      *

      * @deprecated  This method is inherently unsafe.  It may result in

      *      finalizers being called on live objects while other threads are

      *      concurrently manipulating those objects, resulting in erratic

      *      behavior or deadlock.

      * @param value indicating enabling or disabling of finalization

      * @throws  SecurityException

      *        if a security manager exists and its <code>checkExit</code>

      *        method doesn't allow the exit.

      *

      * @see     java.lang.Runtime#exit(int)

      * @see     java.lang.Runtime#gc()

      * @see     java.lang.SecurityManager#checkExit(int)

      * @since   JDK1.1

      */

     @Deprecated

     public static void runFinalizersOnExit(boolean value) {

         Runtime.getRuntime().runFinalizersOnExit(value);

     }

     /**

      * Loads a code file with the specified filename from the local file

      * system as a dynamic library. The filename

      * argument must be a complete path name.

      * <p>

      * The call <code>System.load(name)</code> is effectively equivalent

      * to the call:

      * <blockquote><pre>

      * Runtime.getRuntime().load(name)

      * </pre></blockquote>

      *

      * @param      filename   the file to load.

      * @exception  SecurityException  if a security manager exists and its

      *             <code>checkLink</code> method doesn't allow

      *             loading of the specified dynamic library

      * @exception  UnsatisfiedLinkError  if the file does not exist.

      * @exception  NullPointerException if <code>filename</code> is

      *             <code>null</code>

      * @see        java.lang.Runtime#load(java.lang.String)

      * @see        java.lang.SecurityManager#checkLink(java.lang.String)

      */

     public static void load(String filename) {

         Runtime.getRuntime().load0(getCallerClass(), filename);

     }

     /**

      * Loads the system library specified by the <code>libname</code>

      * argument. The manner in which a library name is mapped to the

      * actual system library is system dependent.

      * <p>

      * The call <code>System.loadLibrary(name)</code> is effectively

      * equivalent to the call

      * <blockquote><pre>

      * Runtime.getRuntime().loadLibrary(name)

      * </pre></blockquote>

      *

      * @param      libname   the name of the library.

      * @exception  SecurityException  if a security manager exists and its

      *             <code>checkLink</code> method doesn't allow

      *             loading of the specified dynamic library

      * @exception  UnsatisfiedLinkError  if the library does not exist.

      * @exception  NullPointerException if <code>libname</code> is

      *             <code>null</code>

      * @see        java.lang.Runtime#loadLibrary(java.lang.String)

      * @see        java.lang.SecurityManager#checkLink(java.lang.String)

      */

     public static void loadLibrary(String libname) {

         Runtime.getRuntime().loadLibrary0(getCallerClass(), libname);

     }

     /**

      * Maps a library name into a platform-specific string representing

      * a native library.

      *

      * @param      libname the name of the library.

      * @return     a platform-dependent native library name.

      * @exception  NullPointerException if <code>libname</code> is

      *             <code>null</code>

      * @see        java.lang.System#loadLibrary(java.lang.String)

      * @see        java.lang.ClassLoader#findLibrary(java.lang.String)

      * @since      1.2

      */

     public static native String mapLibraryName(String libname);

     /**

      * Initialize the system class.  Called after thread initialization.

      */

     private static void initializeSystemClass() {

         // VM might invoke JNU_NewStringPlatform() to set those encoding

         // sensitive properties (user.home, user.name, boot.class.path, etc.)

         // during "props" initialization, in which it may need access, via

         // System.getProperty(), to the related system encoding property that

         // have been initialized (put into "props") at early stage of the

         // initialization. So make sure the "props" is available at the

         // very beginning of the initialization and all system properties to

         // be put into it directly.

         props = new Properties();

         initProperties(props);  // initialized by the VM

         // There are certain system configurations that may be controlled by

         // VM options such as the maximum amount of direct memory and

         // Integer cache size used to support the object identity semantics

         // of autoboxing.  Typically, the library will obtain these values

         // from the properties set by the VM.  If the properties are for

         // internal implementation use only, these properties should be

         // removed from the system properties.

         //

         // See java.lang.Integer.IntegerCache and the

         // sun.misc.VM.saveAndRemoveProperties method for example.

         //

         // Save a private copy of the system properties object that

         // can only be accessed by the internal implementation.  Remove

         // certain system properties that are not intended for public access.

         sun.misc.VM.saveAndRemoveProperties(props);

         lineSeparator = props.getProperty("line.separator");

         sun.misc.Version.init();

         FileInputStream fdIn = new FileInputStream(FileDescriptor.in);

         FileOutputStream fdOut = new FileOutputStream(FileDescriptor.out);

         FileOutputStream fdErr = new FileOutputStream(FileDescriptor.err);

         setIn0(new BufferedInputStream(fdIn));

         setOut0(new PrintStream(new BufferedOutputStream(fdOut, 128), true));

         setErr0(new PrintStream(new BufferedOutputStream(fdErr, 128), true));

         // Load the zip library now in order to keep java.util.zip.ZipFile

         // from trying to use itself to load this library later.

         loadLibrary("zip");

         // Setup Java signal handlers for HUP, TERM, and INT (where available).

         Terminator.setup();

         // Initialize any miscellenous operating system settings that need to be

         // set for the class libraries. Currently this is no-op everywhere except

         // for Windows where the process-wide error mode is set before the java.io

         // classes are used.

         sun.misc.VM.initializeOSEnvironment();

         // Subsystems that are invoked during initialization can invoke

         // sun.misc.VM.isBooted() in order to avoid doing things that should

         // wait until the application class loader has been set up.

         sun.misc.VM.booted();

         // The main thread is not added to its thread group in the same

         // way as other threads; we must do it ourselves here.

         Thread current = Thread.currentThread();

         current.getThreadGroup().add(current);

         // register shared secrets

         setJavaLangAccess();

     }

     private static void setJavaLangAccess() {

         // Allow privileged classes outside of java.lang

         sun.misc.SharedSecrets.setJavaLangAccess(new sun.misc.JavaLangAccess(){

             public sun.reflect.ConstantPool getConstantPool(Class klass) {

                 return klass.getConstantPool();

             }

             public void setAnnotationType(Class klass, AnnotationType type) {

                 klass.setAnnotationType(type);

             }

             public AnnotationType getAnnotationType(Class klass) {

                 return klass.getAnnotationType();

             }

             public <E extends Enum<E>>

                     E[] getEnumConstantsShared(Class<E> klass) {

                 return klass.getEnumConstantsShared();

             }

             public void blockedOn(Thread t, Interruptible b) {

                 t.blockedOn(b);

             }

             public void registerShutdownHook(int slot, boolean registerShutdownInProgress, Runnable hook) {

                 Shutdown.add(slot, registerShutdownInProgress, hook);

             }

             public int getStackTraceDepth(Throwable t) {

                 return t.getStackTraceDepth();

             }

             public StackTraceElement getStackTraceElement(Throwable t, int i) {

                 return t.getStackTraceElement(i);

             }

         });

     }

     /* returns the class of the caller. */

     static Class<?> getCallerClass() {

         // NOTE use of more generic Reflection.getCallerClass()

         return Reflection.getCallerClass(3);

     }

 }