system.java

gcc的组建

   * <dt>line.separator</dt>       <dd>Line separator ("\n" on Unix)</dd>
   * <dt>user.name</dt>            <dd>User account name</dd>
   * <dt>user.home</dt>            <dd>User home directory</dd>
   * <dt>user.dir</dt>             <dd>User's current working directory</dd>
   * </dl>
   *
   * In addition, gnu defines several other properties, where ? stands for
   * each character in '0' through '9':
   * <dl>
   * <dt>gnu.classpath.home</dt>         <dd>Path to the classpath libraries.</dd>
   * <dt>gnu.classpath.version</dt>      <dd>Version of the classpath libraries.</dd>
   * <dt>gnu.classpath.vm.shortname</dt> <dd>Succinct version of the VM name;
   *     used for finding property files in file system</dd>
   * <dt>gnu.classpath.home.url</dt>     <dd> Base URL; used for finding
   *     property files in file system</dd>
   * <dt>gnu.cpu.endian</dt>             <dd>big or little</dd>
   * <dt>gnu.java.io.encoding_scheme_alias.ISO-8859-?</dt>   <dd>8859_?</dd>
   * <dt>gnu.java.io.encoding_scheme_alias.iso-8859-?</dt>   <dd>8859_?</dd>
   * <dt>gnu.java.io.encoding_scheme_alias.iso8859_?</dt>    <dd>8859_?</dd>
   * <dt>gnu.java.io.encoding_scheme_alias.iso-latin-_?</dt> <dd>8859_?</dd>
   * <dt>gnu.java.io.encoding_scheme_alias.latin?</dt>       <dd>8859_?</dd>
   * <dt>gnu.java.io.encoding_scheme_alias.UTF-8</dt>        <dd>UTF8</dd>
   * <dt>gnu.java.io.encoding_scheme_alias.utf-8</dt>        <dd>UTF8</dd>
   * </dl>
   *
   * @return the system properties, will never be null
   * @throws SecurityException if permission is denied
   */
  public static Properties getProperties()
  {
    SecurityManager sm = SecurityManager.current; // Be thread-safe.
    if (sm != null)
      sm.checkPropertiesAccess();
    return SystemProperties.getProperties();
  }

  /**
   * 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 = SecurityManager.current; // Be thread-safe.
    if (sm != null)
      sm.checkPropertiesAccess();
    SystemProperties.setProperties(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 = SecurityManager.current; // Be thread-safe.
    if (sm != null)
      sm.checkPropertyAccess(key);
    else if (key.length() == 0)
      throw new IllegalArgumentException("key can't be empty");
    return SystemProperties.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 = SecurityManager.current; // Be thread-safe.
    if (sm != null)
      sm.checkPropertyAccess(key);
    return SystemProperties.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 = SecurityManager.current; // Be thread-safe.
    if (sm != null)
      sm.checkPermission(new PropertyPermission(key, "write"));
    return SystemProperties.setProperty(key, value);
  }

  /**
   * Gets the value of an environment variable.
   *
   * @param name the name of the environment variable
   * @return the string value of the variable or null when the
   *         environment variable is not defined.
   * @throws NullPointerException
   * @throws SecurityException if permission is denied
   * @since 1.5
   * @specnote This method was deprecated in some JDK releases, but
   *           was restored in 1.5.
   */
  public static String getenv(String name)
  {
    if (name == null)
      throw new NullPointerException();
    SecurityManager sm = SecurityManager.current; // Be thread-safe.
    if (sm != null)
      sm.checkPermission(new RuntimePermission("getenv." + name));
    return getenv0(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>.
   *
   * <p>
   * The library is loaded using the class loader associated with the
   * class associated with the invoking method.
   *
   * @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>.
   *
   * <p>
   * The library is loaded using the class loader associated with the
   * class associated with the invoking method.
   *
   * @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);
  }

  /**
   * 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);

  /**
   * Gets the value of an environment variable.
   *
   * @see #getenv(String)
   */
  static native String getenv0(String name);
} // class System