runtime.java

This is a resource based on j2me embedded,if you dont understand,you can connection with me .

/*
 * @(#)Runtime.java	1.65 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program 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.   
 *   
 * This program 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 at /legal/license.txt).   
 *   
 * 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 Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */

package java.lang;

import java.io.*;
import java.util.StringTokenizer;

/**
 * Every Java application has a single instance of class 
 * <code>Runtime</code> that allows the application to interface with 
 * the environment in which the application is running. The current 
 * runtime can be obtained from the <code>getRuntime</code> method. 
 * <p>
 * An application cannot create its own instance of this class. 
 *
 * @author  unascribed
 * @version 1.57, 05/03/00
 * @see     java.lang.Runtime#getRuntime()
 * @since   JDK1.0
 */

public class Runtime {
    private static Runtime currentRuntime = new Runtime();

    /**
     * Returns the runtime object associated with the current Java application.
     * Most of the methods of class <code>Runtime</code> are instance 
     * methods and must be invoked with respect to the current runtime object. 
     * 
     * @return  the <code>Runtime</code> object associated with the current
     *          Java application.
     */
    public static Runtime getRuntime() { 
	return currentRuntime;
    }

    /** Don't let anyone else instantiate this class */
    private Runtime() {}

    /**
     * Terminates the currently running Java virtual machine by initiating its
     * shutdown sequence.  This method never returns normally.  The argument
     * serves as a status code; by convention, a nonzero status code indicates
     * abnormal termination.
     *
     * <p> The virtual machine's shutdown sequence consists of two phases.  In
     * the first phase all registered {@link #addShutdownHook shutdown hooks},
     * if any, are started in some unspecified order and allowed to run
     * concurrently until they finish.  In the second phase all uninvoked
     * finalizers are run if finalization-on-exit
     * has been enabled.  Once this is done the virtual machine {@link #halt
     * halts}.
     *
     * <p> If this method is invoked after the virtual machine has begun its
     * shutdown sequence then if shutdown hooks are being run this method will
     * block indefinitely.  If shutdown hooks have already been run and on-exit
     * finalization has been enabled then this method halts the virtual machine
     * with the given status code if the status is nonzero; otherwise, it
     * blocks indefinitely.
     *
     * <p> The <tt>{@link System#exit(int) System.exit}</tt> method is the
     * conventional and convenient means of invoking this method. <p>
     *
     * If process model exists, Runtime.exit() must rely on the process 
     * exiting to release resources.
     * <p>
     * If process model does not exist, and a security manager exists,
     * the security manager by default must prohibit calls to Runtime.exit() 
     * by throwing SecurityException.  Otherwise, the system will hang 
     * indefinitely when called.
     * <p>
     * @param  status
     *         Termination status.  By convention, a nonzero status code
     *         indicates abnormal termination.
     *
     * @throws SecurityException
     *         If a security manager is present and its <tt>{@link
     *         SecurityManager#checkExit checkExit}</tt> method does not permit
     *         exiting with the specified status
     *
     * @see java.lang.SecurityException
     * @see java.lang.SecurityManager#checkExit(int)
     * @see #addShutdownHook
     * @see #removeShutdownHook
     * @see #halt(int)
     */
    public void exit(int status) {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkExit(status);
	}
	if (!safeExit(status)) {
	    Shutdown.exit(status);
	}
    }

    private static native boolean safeExit(int status);

    /**
     * Registers a new virtual-machine shutdown hook.
     *
     * <p> The Java virtual machine <i>shuts down</i> in response to two kinds
     * of events:
     *
     *   <ul>
     *
     *   <p> <li> The program <i>exits</i> normally, when the last non-daemon
     *   thread exits or when the <tt>{@link #exit exit}</tt> (equivalently,
     *   <tt>{@link System#exit(int) System.exit}</tt>) method is invoked, or
     *
     *   <p> <li> The virtual machine is <i>terminated</i> in response to a
     *   user interrupt, such as typing <tt>^C</tt>, or a system-wide event,
     *   such as user logoff or system shutdown.
     *
     *   </ul>
     *
     * <p> A <i>shutdown hook</i> is simply an initialized but unstarted
     * thread.  When the virtual machine begins its shutdown sequence it will
     * start all registered shutdown hooks in some unspecified order and let
     * them run concurrently.  When all the hooks have finished it will then
     * run all uninvoked finalizers if finalization-on-exit has been enabled.
     * Finally, the virtual machine will halt.  Note that daemon threads will
     * continue to run during the shutdown sequence, as will non-daemon threads
     * if shutdown was initiated by invoking the <tt>{@link #exit exit}</tt>
     * method.
     *
     * <p> Once the shutdown sequence has begun it can be stopped only by
     * invoking the <tt>{@link #halt halt}</tt> method, which forcibly
     * terminates the virtual machine.
     *
     * <p> Once the shutdown sequence has begun it is impossible to register a
     * new shutdown hook or de-register a previously-registered hook.
     * Attempting either of these operations will cause an
     * <tt>{@link IllegalStateException}</tt> to be thrown.
     *
     * <p> Shutdown hooks run at a delicate time in the life cycle of a virtual
     * machine and should therefore be coded defensively.  They should, in
     * particular, be written to be thread-safe and to avoid deadlocks insofar
     * as possible.  They should also not rely blindly upon services that may
     * have registered their own shutdown hooks and therefore may themselves in
     * the process of shutting down.
     *
     * <p> Shutdown hooks should also finish their work quickly.  When a
     * program invokes <tt>{@link #exit exit}</tt> the expectation is
     * that the virtual machine will promptly shut down and exit.  When the
     * virtual machine is terminated due to user logoff or system shutdown the
     * underlying operating system may only allow a fixed amount of time in
     * which to shut down and exit.  It is therefore inadvisable to attempt any
     * user interaction or to perform a long-running computation in a shutdown
     * hook.
     *
     * <p> Uncaught exceptions are handled in shutdown hooks just as in any
     * other thread, by invoking the <tt>{@link ThreadGroup#uncaughtException
     * uncaughtException}</tt> method of the thread's <tt>{@link
     * ThreadGroup}</tt> object.  The default implementation of this method
     * prints the exception's stack trace to <tt>{@link System#err}</tt> and
     * terminates the thread; it does not cause the virtual machine to exit or
     * halt.
     *
     * <p> In rare circumstances the virtual machine may <i>abort</i>, that is,
     * stop running without shutting down cleanly.  This occurs when the
     * virtual machine is terminated externally, for example with the
     * <tt>SIGKILL</tt> signal on Unix or the <tt>TerminateProcess</tt> call on
     * Microsoft Windows.  The virtual machine may also abort if a native method goes awry
     * by, for example, corrupting internal data structures or attempting to
     * access nonexistent memory.  If the virtual machine aborts then no
     * guarantee can be made about whether or not any shutdown hooks will be
     * run. <p>
     *
     * @param   hook
     *          An initialized but unstarted <tt>{@link Thread}</tt> object
     *
     * @throws  IllegalArgumentException
     *          If the specified hook has already been registered,
     *          or if it can be determined that the hook is already running or
     *          has already been run
     *
     * @throws  IllegalStateException
     *          If the virtual machine is already in the process
     *          of shutting down
     *
     * @throws  SecurityException
     *          If a security manager is present and it denies
     *          <tt>{@link RuntimePermission}("shutdownHooks")</tt>
     *
     * @see #removeShutdownHook
     * @see #halt(int)
     * @see #exit(int)
     * @since 1.3
     */
    public void addShutdownHook(Thread hook) {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	    sm.checkPermission(new RuntimePermission("shutdownHooks"));
	}
	Shutdown.add(hook);
    }

    /**
     * De-registers a previously-registered virtual-machine shutdown hook. <p>
     *
     * @param hook the hook to remove
     * @return <tt>true</tt> if the specified hook had previously been
     * registered and was successfully de-registered, <tt>false</tt>
     * otherwise.
     *
     * @throws  IllegalStateException
     *          If the virtual machine is already in the process of shutting
     *          down
     *
     * @throws  SecurityException
     *          If a security manager is present and it denies
     *          <tt>{@link RuntimePermission}("shutdownHooks")</tt>
     *
     * @see #addShutdownHook
     * @see #exit(int)
     * @since 1.3
     */
    public boolean removeShutdownHook(Thread hook) {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	    sm.checkPermission(new RuntimePermission("shutdownHooks"));
	}
	return Shutdown.remove(hook);
    }

    /**
     * Forcibly terminates the currently running Java virtual machine.  This
     * method never returns normally.
     *
     * <p> This method should be used with extreme caution.  Unlike the
     * <tt>{@link #exit exit}</tt> method, this method does not cause shutdown
     * hooks to be started and does not run uninvoked finalizers if
     * finalization-on-exit has been enabled.  If the shutdown sequence has
     * already been initiated then this method does not wait for any running
     * shutdown hooks or finalizers to finish their work. <p>
     *
     * If process model exists, Runtime.halt() must rely on the process 
     * exiting to release resources.
     * <p>
     * If process model does not exist, and a security manager exists,
     * the security manager by default must prohibit calls to Runtime.halt() 
     * by throwing SecurityException.  Otherwise, the system will hang 
     * indefinitely when called.
     * <p>
     *
     * @param  status
     *         Termination status.  By convention, a nonzero status code
     *         indicates abnormal termination.  If the <tt>{@link Runtime#exit
     *         exit}</tt> (equivalently, <tt>{@link System#exit(int)
     *         System.exit}</tt>) method has already been invoked then this
     *         status code will override the status code passed to that method.
     *
     * @throws SecurityException
     *         If a security manager is present and its <tt>{@link
     *         SecurityManager#checkExit checkExit}</tt> method does not permit
     *         an exit with the specified status
     *
     * @see #exit
     * @see #addShutdownHook
     * @see #removeShutdownHook
     * @since 1.3
     */
    public void halt(int status) {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	    sm.checkExit(status);
	}
	Shutdown.halt(status);
    }

    /**
     * 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.
     *
     * param value true to enable finalization on exit, false to disable
     * 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.