Runtime.exec()

关于RunTime类的介绍：

 /**
  * 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
  * @see     java.lang.Runtime#getRuntime()
  * @since   JDK1.0
  */

 public class Runtime {
     ......
 }

RunTime类

类具体的定义：

 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 {@link #runFinalizersOnExit 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>
      *
      * @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 #runFinalizersOnExit
      * @see #halt(int)
      */
     public void exit(int status) {
         SecurityManager security = System.getSecurityManager();
         if (security != null) {
             security.checkExit(status);
         }
         Shutdown.exit(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>
      *
      *   <li> The program <i>exits</i> normally, when the last non-daemon
      *   thread exits or when the <tt>{@link #exit exit}</tt> (equivalently,
      *   {@link System#exit(int) System.exit}) method is invoked, or
      *
      *   <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.  Attempts to use other thread-based
      * services such as the AWT event-dispatch thread, for example, may lead to
      * deadlocks.
      *
      * <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"));
         }
         ApplicationShutdownHooks.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 ApplicationShutdownHooks.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>
      *
      * @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.
      *
      * @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) {
         SecurityManager security = System.getSecurityManager();
         if (security != null) {
             try {
                 security.checkExit(0);
             } catch (SecurityException e) {
                 throw new SecurityException("runFinalizersOnExit");
             }
         }
         Shutdown.setRunFinalizersOnExit(value);
     }

     /**
      * Executes the specified string command in a separate process.
      *
      * <p>This is a convenience method.  An invocation of the form
      * <tt>exec(command)</tt>
      * behaves in exactly the same way as the invocation
      * <tt>{@link #exec(String, String[], File) exec}(command, null, null)</tt>.
      *
      * @param   command   a specified system command.
      *
      * @return  A new {@link Process} object for managing the subprocess
      *
      * @throws  SecurityException
      *          If a security manager exists and its
      *          {@link SecurityManager#checkExec checkExec}
      *          method doesn't allow creation of the subprocess
      *
      * @throws  IOException
      *          If an I/O error occurs
      *
      * @throws  NullPointerException
      *          If <code>command</code> is <code>null</code>
      *
      * @throws  IllegalArgumentException
      *          If <code>command</code> is empty
      *
      * @see     #exec(String[], String[], File)
      * @see     ProcessBuilder
      */
     public Process exec(String command) throws IOException {
         return exec(command, null, null);
     }

     /**
      * Executes the specified string command in a separate process with the
      * specified environment.
      *
      * <p>This is a convenience method.  An invocation of the form
      * <tt>exec(command, envp)</tt>
      * behaves in exactly the same way as the invocation
      * <tt>{@link #exec(String, String[], File) exec}(command, envp, null)</tt>.
      *
      * @param   command   a specified system command.
      *
      * @param   envp      array of strings, each element of which
      *                    has environment variable settings in the format
      *                    <i>name</i>=<i>value</i>, or
      *                    <tt>null</tt> if the subprocess should inherit
      *                    the environment of the current process.
      *
      * @return  A new {@link Process} object for managing the subprocess
      *
      * @throws  SecurityException
      *          If a security manager exists and its
      *          {@link SecurityManager#checkExec checkExec}
      *          method doesn't allow creation of the subprocess
      *
      * @throws  IOException
      *          If an I/O error occurs
      *
      * @throws  NullPointerException
      *          If <code>command</code> is <code>null</code>,
      *          or one of the elements of <code>envp</code> is <code>null</code>
      *
      * @throws  IllegalArgumentException
      *          If <code>command</code> is empty
      *
      * @see     #exec(String[], String[], File)
      * @see     ProcessBuilder
      */
     public Process exec(String command, String[] envp) throws IOException {
         return exec(command, envp, null);
     }

     /**
      * Executes the specified string command in a separate process with the
      * specified environment and working directory.
      *
      * <p>This is a convenience method.  An invocation of the form
      * <tt>exec(command, envp, dir)</tt>
      * behaves in exactly the same way as the invocation
      * <tt>{@link #exec(String[], String[], File) exec}(cmdarray, envp, dir)</tt>,
      * where <code>cmdarray</code> is an array of all the tokens in
      * <code>command</code>.
      *
      * <p>More precisely, the <code>command</code> string is broken
      * into tokens using a {@link StringTokenizer} created by the call
      * <code>new {@link StringTokenizer}(command)</code> with no
      * further modification of the character categories.  The tokens
      * produced by the tokenizer are then placed in the new string
      * array <code>cmdarray</code>, in the same order.
      *
      * @param   command   a specified system command.
      *
      * @param   envp      array of strings, each element of which
      *                    has environment variable settings in the format
      *                    <i>name</i>=<i>value</i>, or
      *                    <tt>null</tt> if the subprocess should inherit
      *                    the environment of the current process.
      *
      * @param   dir       the working directory of the subprocess, or
      *                    <tt>null</tt> if the subprocess should inherit
      *                    the working directory of the current process.
      *
      * @return  A new {@link Process} object for managing the subprocess
      *
      * @throws  SecurityException
      *          If a security manager exists and its
      *          {@link SecurityManager#checkExec checkExec}
      *          method doesn't allow creation of the subprocess
      *
      * @throws  IOException
      *          If an I/O error occurs
      *
      * @throws  NullPointerException
      *          If <code>command</code> is <code>null</code>,
      *          or one of the elements of <code>envp</code> is <code>null</code>
      *
      * @throws  IllegalArgumentException
      *          If <code>command</code> is empty
      *
      * @see     ProcessBuilder
      * @since 1.3
      */
     public Process exec(String command, String[] envp, File dir)
         throws IOException {
         if (command.length() == 0)
             throw new IllegalArgumentException("Empty command");

         StringTokenizer st = new StringTokenizer(command);
         String[] cmdarray = new String[st.countTokens()];
         for (int i = 0; st.hasMoreTokens(); i++)
             cmdarray[i] = st.nextToken();
         return exec(cmdarray, envp, dir);
     }

     /**
      * Executes the specified command and arguments in a separate process.
      *
      * <p>This is a convenience method.  An invocation of the form
      * <tt>exec(cmdarray)</tt>
      * behaves in exactly the same way as the invocation
      * <tt>{@link #exec(String[], String[], File) exec}(cmdarray, null, null)</tt>.
      *
      * @param   cmdarray  array containing the command to call and
      *                    its arguments.
      *
      * @return  A new {@link Process} object for managing the subprocess
      *
      * @throws  SecurityException
      *          If a security manager exists and its
      *          {@link SecurityManager#checkExec checkExec}
      *          method doesn't allow creation of the subprocess
      *
      * @throws  IOException
      *          If an I/O error occurs
      *
      * @throws  NullPointerException
      *          If <code>cmdarray</code> is <code>null</code>,
      *          or one of the elements of <code>cmdarray</code> is <code>null</code>
      *
      * @throws  IndexOutOfBoundsException
      *          If <code>cmdarray</code> is an empty array
      *          (has length <code>0</code>)
      *
      * @see     ProcessBuilder
      */
     public Process exec(String cmdarray[]) throws IOException {
         return exec(cmdarray, null, null);
     }

     /**
      * Executes the specified command and arguments in a separate process
      * with the specified environment.
      *
      * <p>This is a convenience method.  An invocation of the form
      * <tt>exec(cmdarray, envp)</tt>
      * behaves in exactly the same way as the invocation
      * <tt>{@link #exec(String[], String[], File) exec}(cmdarray, envp, null)</tt>.
      *
      * @param   cmdarray  array containing the command to call and
      *                    its arguments.
      *
      * @param   envp      array of strings, each element of which
      *                    has environment variable settings in the format
      *                    <i>name</i>=<i>value</i>, or
      *                    <tt>null</tt> if the subprocess should inherit
      *                    the environment of the current process.
      *
      * @return  A new {@link Process} object for managing the subprocess
      *
      * @throws  SecurityException
      *          If a security manager exists and its
      *          {@link SecurityManager#checkExec checkExec}
      *          method doesn't allow creation of the subprocess
      *
      * @throws  IOException
      *          If an I/O error occurs
      *
      * @throws  NullPointerException
      *          If <code>cmdarray</code> is <code>null</code>,
      *          or one of the elements of <code>cmdarray</code> is <code>null</code>,
      *          or one of the elements of <code>envp</code> is <code>null</code>
      *
      * @throws  IndexOutOfBoundsException
      *          If <code>cmdarray</code> is an empty array
      *          (has length <code>0</code>)
      *
      * @see     ProcessBuilder
      */
     public Process exec(String[] cmdarray, String[] envp) throws IOException {
         return exec(cmdarray, envp, null);
     }

     /**
      * Executes the specified command and arguments in a separate process with
      * the specified environment and working directory.
      *
      * <p>Given an array of strings <code>cmdarray</code>, representing the
      * tokens of a command line, and an array of strings <code>envp</code>,
      * representing "environment" variable settings, this method creates
      * a new process in which to execute the specified command.
      *
      * <p>This method checks that <code>cmdarray</code> is a valid operating
      * system command.  Which commands are valid is system-dependent,
      * but at the very least the command must be a non-empty list of
      * non-null strings.
      *
      * <p>If <tt>envp</tt> is <tt>null</tt>, the subprocess inherits the
      * environment settings of the current process.
      *
      * <p>A minimal set of system dependent environment variables may
      * be required to start a process on some operating systems.
      * As a result, the subprocess may inherit additional environment variable
      * settings beyond those in the specified environment.
      *
      * <p>{@link ProcessBuilder#start()} is now the preferred way to
      * start a process with a modified environment.
      *
      * <p>The working directory of the new subprocess is specified by <tt>dir</tt>.
      * If <tt>dir</tt> is <tt>null</tt>, the subprocess inherits the
      * current working directory of the current process.
      *
      * <p>If a security manager exists, its
      * {@link SecurityManager#checkExec checkExec}
      * method is invoked with the first component of the array
      * <code>cmdarray</code> as its argument. This may result in a
      * {@link SecurityException} being thrown.
      *
      * <p>Starting an operating system process is highly system-dependent.
      * Among the many things that can go wrong are:
      * <ul>
      * <li>The operating system program file was not found.
      * <li>Access to the program file was denied.
      * <li>The working directory does not exist.
      * </ul>
      *
      * <p>In such cases an exception will be thrown.  The exact nature
      * of the exception is system-dependent, but it will always be a
      * subclass of {@link IOException}.
      *
      *
      * @param   cmdarray  array containing the command to call and
      *                    its arguments.
      *
      * @param   envp      array of strings, each element of which
      *                    has environment variable settings in the format
      *                    <i>name</i>=<i>value</i>, or
      *                    <tt>null</tt> if the subprocess should inherit
      *                    the environment of the current process.
      *
      * @param   dir       the working directory of the subprocess, or
      *                    <tt>null</tt> if the subprocess should inherit
      *                    the working directory of the current process.
      *
      * @return  A new {@link Process} object for managing the subprocess
      *
      * @throws  SecurityException
      *          If a security manager exists and its
      *          {@link SecurityManager#checkExec checkExec}
      *          method doesn't allow creation of the subprocess
      *
      * @throws  IOException
      *          If an I/O error occurs
      *
      * @throws  NullPointerException
      *          If <code>cmdarray</code> is <code>null</code>,
      *          or one of the elements of <code>cmdarray</code> is <code>null</code>,
      *          or one of the elements of <code>envp</code> is <code>null</code>
      *
      * @throws  IndexOutOfBoundsException
      *          If <code>cmdarray</code> is an empty array
      *          (has length <code>0</code>)
      *
      * @see     ProcessBuilder
      * @since 1.3
      */
     public Process exec(String[] cmdarray, String[] envp, File dir)
         throws IOException {
         return new ProcessBuilder(cmdarray)
             .environment(envp)
             .directory(dir)
             .start();
     }

     /**
      * Returns the number of processors available to the Java virtual machine.
      *
      * <p> This value may change during a particular invocation of the virtual
      * machine.  Applications that are sensitive to the number of available
      * processors should therefore occasionally poll this property and adjust
      * their resource usage appropriately. </p>
      *
      * @return  the maximum number of processors available to the virtual
      *          machine; never smaller than one
      * @since 1.4
      */
     public native int availableProcessors();

     /**
      * Returns the amount of free memory in the Java Virtual Machine.
      * Calling the
      * <code>gc</code> method may result in increasing the value returned
      * by <code>freeMemory.</code>
      *
      * @return  an approximation to the total amount of memory currently
      *          available for future allocated objects, measured in bytes.
      */
     public native long freeMemory();

     /**
      * Returns the total amount of memory in the Java virtual machine.
      * The value returned by this method may vary over time, depending on
      * the host environment.
      * <p>
      * Note that the amount of memory required to hold an object of any
      * given type may be implementation-dependent.
      *
      * @return  the total amount of memory currently available for current
      *          and future objects, measured in bytes.
      */
     public native long totalMemory();

     /**
      * Returns the maximum amount of memory that the Java virtual machine will
      * attempt to use.  If there is no inherent limit then the value {@link
      * java.lang.Long#MAX_VALUE} will be returned.
      *
      * @return  the maximum amount of memory that the virtual machine will
      *          attempt to use, measured in bytes
      * @since 1.4
      */
     public native long maxMemory();

     /**
      * Runs the garbage collector.
      * Calling this 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 virtual machine has made
      * its best effort to recycle all discarded objects.
      * <p>
      * The name <code>gc</code> stands for "garbage
      * collector". The virtual machine performs this recycling
      * process automatically as needed, in a separate thread, even if the
      * <code>gc</code> method is not invoked explicitly.
      * <p>
      * The method {@link System#gc()} is the conventional and convenient
      * means of invoking this method.
      */
     public native void gc();

     /* Wormhole for calling java.lang.ref.Finalizer.runFinalization */
     private static native void runFinalization0();

     /**
      * Runs the finalization methods of any objects pending finalization.
      * 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 virtual machine has made a best effort to
      * complete all outstanding finalizations.
      * <p>
      * The virtual machine performs the finalization process
      * automatically as needed, in a separate thread, if the
      * <code>runFinalization</code> method is not invoked explicitly.
      * <p>
      * The method {@link System#runFinalization()} is the conventional
      * and convenient means of invoking this method.
      *
      * @see     java.lang.Object#finalize()
      */
     public void runFinalization() {
         runFinalization0();
     }

     /**
      * Enables/Disables tracing of instructions.
      * If the <code>boolean</code> argument is <code>true</code>, this
      * method suggests that the Java virtual machine emit debugging
      * information for each instruction in the virtual machine as it
      * is executed. The format of this information, and the file or other
      * output stream to which it is emitted, depends on the host environment.
      * The virtual machine may ignore this request if it does not support
      * this feature. The destination of the trace output is system
      * dependent.
      * <p>
      * If the <code>boolean</code> argument is <code>false</code>, this
      * method causes the virtual machine to stop performing the
      * detailed instruction trace it is performing.
      *
      * @param   on   <code>true</code> to enable instruction tracing;
      *               <code>false</code> to disable this feature.
      */
     public native void traceInstructions(boolean on);

     /**
      * Enables/Disables tracing of method calls.
      * If the <code>boolean</code> argument is <code>true</code>, this
      * method suggests that the Java virtual machine emit debugging
      * information for each method in the virtual machine as it is
      * called. The format of this information, and the file or other output
      * stream to which it is emitted, depends on the host environment. The
      * virtual machine may ignore this request if it does not support
      * this feature.
      * <p>
      * Calling this method with argument false suggests that the
      * virtual machine cease emitting per-call debugging information.
      *
      * @param   on   <code>true</code> to enable instruction tracing;
      *               <code>false</code> to disable this feature.
      */
     public native void traceMethodCalls(boolean on);

     /**
      * Loads the native library specified by the filename argument.  The filename
      * argument must be an absolute path name.
      * (for example
      * <code>Runtime.getRuntime().load("/home/avh/lib/libX11.so");</code>).
      *
      * If the filename argument, when stripped of any platform-specific library
      * prefix, path, and file extension, indicates a library whose name is,
      * for example, L, and a native library called L is statically linked
      * with the VM, then the JNI_OnLoad_L function exported by the library
      * is invoked rather than attempting to load a dynamic library.
      * A filename matching the argument does not have to exist in the file
      * system. See the JNI Specification for more details.
      *
      * Otherwise, the filename argument is mapped to a native library image in
      * an implementation-dependent manner.
      * <p>
      * First, if there is a security manager, its <code>checkLink</code>
      * method is called with the <code>filename</code> as its argument.
      * This may result in a security exception.
      * <p>
      * This is similar to the method {@link #loadLibrary(String)}, but it
      * accepts a general file name as an argument rather than just a library
      * name, allowing any file of native code to be loaded.
      * <p>
      * The method {@link System#load(String)} is the conventional and
      * convenient means of invoking this method.
      *
      * @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 either the filename is not an
      *             absolute path name, the native library is not statically
      *             linked with the VM, or the library cannot be mapped to
      *             a native library image by the host system.
      * @exception  NullPointerException if <code>filename</code> is
      *             <code>null</code>
      * @see        java.lang.Runtime#getRuntime()
      * @see        java.lang.SecurityException
      * @see        java.lang.SecurityManager#checkLink(java.lang.String)
      */
     @CallerSensitive
     public void load(String filename) {
         load0(Reflection.getCallerClass(), filename);
     }

     synchronized void load0(Class<?> fromClass, String filename) {
         SecurityManager security = System.getSecurityManager();
         if (security != null) {
             security.checkLink(filename);
         }
         if (!(new File(filename).isAbsolute())) {
             throw new UnsatisfiedLinkError(
                 "Expecting an absolute path of the library: " + filename);
         }
         ClassLoader.loadLibrary(fromClass, filename, true);
     }

     /**
      * Loads the native library specified by the <code>libname</code>
      * argument.  The <code>libname</code> argument must not contain any platform
      * specific prefix, file extension or path. If a native library
      * called <code>libname</code> is statically linked with the VM, then the
      * JNI_OnLoad_<code>libname</code> function exported by the library is invoked.
      * See the JNI Specification for more details.
      *
      * Otherwise, the libname argument is loaded from a system library
      * location and mapped to a native library image in an implementation-
      * dependent manner.
      * <p>
      * First, if there is a security manager, its <code>checkLink</code>
      * method is called with the <code>libname</code> as its argument.
      * This may result in a security exception.
      * <p>
      * The method {@link System#loadLibrary(String)} is the conventional
      * and convenient means of invoking this method. If native
      * methods are to be used in the implementation of a class, a standard
      * strategy is to put the native code in a library file (call it
      * <code>LibFile</code>) and then to put a static initializer:
      * <blockquote><pre>
      * static { System.loadLibrary("LibFile"); }
      * </pre></blockquote>
      * within the class declaration. When the class is loaded and
      * initialized, the necessary native code implementation for the native
      * methods will then be loaded as well.
      * <p>
      * If this method is called more than once with the same library
      * name, the second and subsequent calls are ignored.
      *
      * @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 either the libname argument
      *             contains a file path, the native library is not statically
      *             linked with the VM,  or the library cannot be mapped to a
      *             native library image by the host system.
      * @exception  NullPointerException if <code>libname</code> is
      *             <code>null</code>
      * @see        java.lang.SecurityException
      * @see        java.lang.SecurityManager#checkLink(java.lang.String)
      */
     @CallerSensitive
     public void loadLibrary(String libname) {
         loadLibrary0(Reflection.getCallerClass(), libname);
     }

     synchronized void loadLibrary0(Class<?> fromClass, String libname) {
         SecurityManager security = System.getSecurityManager();
         if (security != null) {
             security.checkLink(libname);
         }
         if (libname.indexOf((int)File.separatorChar) != -1) {
             throw new UnsatisfiedLinkError(
     "Directory separator should not appear in library name: " + libname);
         }
         ClassLoader.loadLibrary(fromClass, libname, false);
     }

     /**
      * Creates a localized version of an input stream. This method takes
      * an <code>InputStream</code> and returns an <code>InputStream</code>
      * equivalent to the argument in all respects except that it is
      * localized: as characters in the local character set are read from
      * the stream, they are automatically converted from the local
      * character set to Unicode.
      * <p>
      * If the argument is already a localized stream, it may be returned
      * as the result.
      *
      * @param      in InputStream to localize
      * @return     a localized input stream
      * @see        java.io.InputStream
      * @see        java.io.BufferedReader#BufferedReader(java.io.Reader)
      * @see        java.io.InputStreamReader#InputStreamReader(java.io.InputStream)
      * @deprecated As of JDK&nbsp;1.1, the preferred way to translate a byte
      * stream in the local encoding into a character stream in Unicode is via
      * the <code>InputStreamReader</code> and <code>BufferedReader</code>
      * classes.
      */
     @Deprecated
     public InputStream getLocalizedInputStream(InputStream in) {
         return in;
     }

     /**
      * Creates a localized version of an output stream. This method
      * takes an <code>OutputStream</code> and returns an
      * <code>OutputStream</code> equivalent to the argument in all respects
      * except that it is localized: as Unicode characters are written to
      * the stream, they are automatically converted to the local
      * character set.
      * <p>
      * If the argument is already a localized stream, it may be returned
      * as the result.
      *
      * @deprecated As of JDK&nbsp;1.1, the preferred way to translate a
      * Unicode character stream into a byte stream in the local encoding is via
      * the <code>OutputStreamWriter</code>, <code>BufferedWriter</code>, and
      * <code>PrintWriter</code> classes.
      *
      * @param      out OutputStream to localize
      * @return     a localized output stream
      * @see        java.io.OutputStream
      * @see        java.io.BufferedWriter#BufferedWriter(java.io.Writer)
      * @see        java.io.OutputStreamWriter#OutputStreamWriter(java.io.OutputStream)
      * @see        java.io.PrintWriter#PrintWriter(java.io.OutputStream)
      */
     @Deprecated
     public OutputStream getLocalizedOutputStream(OutputStream out) {
         return out;
     }

 }

类的内部定义

RunTime.exec() 用来执行特定的

/**
     * Executes the specified string command in a separate process with the
     * specified environment.
     *

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