system.java

俄罗斯高人Mamaich的Pocket gcc编译器（运行在PocketPC上）的全部源代码。

   * allow getting a single property, but not the entire group.
   *
   * <p>The required properties include:
   * <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.vm.specification.version <dd>VM Spec version
   * <dt>java.vm.specification.vendor  <dd>VM Spec vendor
   * <dt>java.vm.specification.name    <dd>VM Spec name
   * <dt>java.vm.version      <dd>VM implementation version
   * <dt>java.vm.vendor       <dd>VM implementation vendor
   * <dt>java.vm.name         <dd>VM implementation name
   * <dt>java.specification.version    <dd>Java Runtime Environment version
   * <dt>java.specification.vendor     <dd>Java Runtime Environment vendor
   * <dt>java.specification.name       <dd>Java Runtime Environment name
   * <dt>java.class.version   <dd>Java class version number
   * <dt>java.class.path      <dd>Java classpath
   * <dt>java.library.path    <dd>Path for finding Java libraries
   * <dt>java.io.tmpdir       <dd>Default temp file path
   * <dt>java.compiler        <dd>Name of JIT to use
   * <dt>java.ext.dirs        <dd>Java extension path
   * <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>
   *
   * In addition, gnu defines several other properties, where ? stands for
   * each character in '0' through '9':
   * <dl>
   * <dl> gnu.classpath.vm.shortname <dd> Succinct version of the VM name;
   *      used for finding property files in file system
   * <dl> gnu.classpath.home.url <dd> Base URL; used for finding
   *      property files in file system
   * <dt> gnu.cpu.endian      <dd>big or little
   * <dt> gnu.java.io.encoding_scheme_alias.ISO-8859-?   <dd>8859_?
   * <dt> gnu.java.io.encoding_scheme_alias.iso-8859-?   <dd>8859_?
   * <dt> gnu.java.io.encoding_scheme_alias.iso8859_?    <dd>8859_?
   * <dt> gnu.java.io.encoding_scheme_alias.iso-latin-_? <dd>8859_?
   * <dt> gnu.java.io.encoding_scheme_alias.latin?       <dd>8859_?
   * <dt> gnu.java.io.encoding_scheme_alias.UTF-8        <dd>UTF8
   * <dt> gnu.java.io.encoding_scheme_alias.utf-8        <dd>UTF8
   * </dl>
   *
   * @return the system properties, will never be null
   * @throws SecurityException if permission is denied
   */
  public static Properties getProperties()
  {
    SecurityManager sm = Runtime.securityManager; // Be thread-safe.
    if (sm != null)
      sm.checkPropertiesAccess();
    return properties;
  }

  /**
   * Set all the system properties at once. A security check may be performed,
   * <code>checkPropertiesAccess</code>. Note that a security manager may
   * allow setting a single property, but not the entire group. An argument
   * of null resets the properties to the startup default.
   *
   * @param properties the new set of system properties
   * @throws SecurityException if permission is denied
   */
  public static void setProperties(Properties properties)
  {
    SecurityManager sm = Runtime.securityManager; // Be thread-safe.
    if (sm != null)
      sm.checkPropertiesAccess();
    if (properties == null)
      {
	// Note that we use clone here and not new.  Some programs
	// assume that the system properties do not have a parent.
	properties = (Properties) Runtime.defaultProperties.clone();
      }
    System.properties = properties;
  }

  /**
   * Get a single system property by name. A security check may be performed,
   * <code>checkPropertyAccess(key)</code>.
   *
   * @param key the name of the system property to get
   * @return the property, or null if not found
   * @throws SecurityException if permission is denied
   * @throws NullPointerException if key is null
   * @throws IllegalArgumentException if key is ""
   */
  public static String getProperty(String key)
  {
    SecurityManager sm = Runtime.securityManager; // Be thread-safe.
    if (sm != null)
      sm.checkPropertyAccess(key);
    else if (key.length() == 0)
      throw new IllegalArgumentException("key can't be empty");
    return properties.getProperty(key);
  }

  /**
   * Get a single system property by name. A security check may be performed,
   * <code>checkPropertyAccess(key)</code>.
   *
   * @param key the name of the system property to get
   * @param def the default
   * @return the property, or def if not found
   * @throws SecurityException if permission is denied
   * @throws NullPointerException if key is null
   * @throws IllegalArgumentException if key is ""
   */
  public static String getProperty(String key, String def)
  {
    SecurityManager sm = Runtime.securityManager; // Be thread-safe.
    if (sm != null)
      sm.checkPropertyAccess(key);
    return properties.getProperty(key, def);
  }

  /**
   * Set a single system property by name. A security check may be performed,
   * <code>checkPropertyAccess(key, "write")</code>.
   *
   * @param key the name of the system property to set
   * @param value the new value
   * @return the previous value, or null
   * @throws SecurityException if permission is denied
   * @throws NullPointerException if key is null
   * @throws IllegalArgumentException if key is ""
   * @since 1.2
   */
  public static String setProperty(String key, String value)
  {
    SecurityManager sm = Runtime.securityManager; // Be thread-safe.
    if (sm != null)
      sm.checkPermission(new PropertyPermission(key, "write"));
    return (String) properties.setProperty(key, value);
  }

  /**
   * This used to get an environment variable, but following Sun's lead,
   * it now throws an Error. Use <code>getProperty</code> instead.
   *
   * @param name the name of the environment variable
   * @return this does not return
   * @throws Error this is not supported
   * @deprecated use {@link #getProperty(String)}; getenv is not supported
   */
  public static String getenv(String name)
  {
    throw new Error("getenv no longer supported, use properties instead: "
                    + name);
  }

  /**
   * Terminate the Virtual Machine. This just calls
   * <code>Runtime.getRuntime().exit(status)</code>, and never returns.
   * Obviously, a security check is in order, <code>checkExit</code>.
   *
   * @param status the exit status; by convention non-zero is abnormal
   * @throws SecurityException if permission is denied
   * @see Runtime#exit(int)
   */
  public static void exit(int status)
  {
    Runtime.getRuntime().exit(status);
  }

  /**
   * Calls the garbage collector. This is only a hint, and it is up to the
   * implementation what this hint suggests, but it usually causes a
   * best-effort attempt to reclaim unused memory from discarded objects.
   * This calls <code>Runtime.getRuntime().gc()</code>.
   *
   * @see Runtime#gc()
   */
  public static void gc()
  {
    Runtime.getRuntime().gc();
  }

  /**
   * Runs object finalization on pending objects. This is only a hint, and
   * it is up to the implementation what this hint suggests, but it usually
   * causes a best-effort attempt to run finalizers on all objects ready
   * to be reclaimed. This calls
   * <code>Runtime.getRuntime().runFinalization()</code>.
   *
   * @see Runtime#runFinalization()
   */
  public static void runFinalization()
  {
    Runtime.getRuntime().runFinalization();
  }

  /**
   * Tell the Runtime whether to run finalization before exiting the
   * JVM.  This is inherently unsafe in multi-threaded applications,
   * since it can force initialization on objects which are still in use
   * by live threads, leading to deadlock; therefore this is disabled by
   * default. There may be a security check, <code>checkExit(0)</code>. This
   * calls <code>Runtime.getRuntime().runFinalizersOnExit()</code>.
   *
   * @param finalizeOnExit whether to run finalizers on exit
   * @throws SecurityException if permission is denied
   * @see Runtime#runFinalizersOnExit()
   * @since 1.1
   * @deprecated never rely on finalizers to do a clean, thread-safe,
   *             mop-up from your code
   */
  public static void runFinalizersOnExit(boolean finalizeOnExit)
  {
    Runtime.getRuntime().runFinalizersOnExit(finalizeOnExit);
  }

  /**
   * Load a code file using its explicit system-dependent filename. A security
   * check may be performed, <code>checkLink</code>. This just calls
   * <code>Runtime.getRuntime().load(filename)</code>.
   *
   * @param filename the code file to load
   * @throws SecurityException if permission is denied
   * @throws UnsatisfiedLinkError if the file cannot be loaded
   * @see Runtime#load(String)
   */
  public static void load(String filename)
  {
    Runtime.getRuntime().load(filename);
  }

  /**
   * Load a library using its explicit system-dependent filename. A security
   * check may be performed, <code>checkLink</code>. This just calls
   * <code>Runtime.getRuntime().load(filename)</code>.
   *
   * @param libname the library file to load
   * @throws SecurityException if permission is denied
   * @throws UnsatisfiedLinkError if the file cannot be loaded
   * @see Runtime#load(String)
   */
  public static void loadLibrary(String libname)
  {
    Runtime.getRuntime().loadLibrary(libname);
  }

  /**
   * Convert a library name to its platform-specific variant.
   *
   * @param libname the library name, as used in <code>loadLibrary</code>
   * @return the platform-specific mangling of the name
   * @since 1.2
   */
  public static String mapLibraryName(String libname)
  {
    // XXX Fix this!!!!
    return Runtime.nativeGetLibname("", libname);
  }

  /**
   * Detect big-endian systems.
   *
   * @return true if the system is big-endian.
   */
  static native boolean isWordsBigEndian();

  /**
   * Set {@link #in} to a new InputStream.
   *
   * @param in the new InputStream
   * @see #setIn(InputStream)
   */
  private static native void setIn0(InputStream in);

  /**
   * Set {@link #out} to a new PrintStream.
   *
   * @param out the new PrintStream
   * @see #setOut(PrintStream)
   */
  private static native void setOut0(PrintStream out);

  /**
   * Set {@link #err} to a new PrintStream.
   *
   * @param err the new PrintStream
   * @see #setErr(PrintStream)
   */
  private static native void setErr0(PrintStream err);
} // class System