An application cannot create its own instance of this class.Since:JDK1.0See Also:getRuntime()Method SummaryAll Methods Static Methods Instance Methods Concrete Methods Deprecated Methods Modifier and TypeMethod and DescriptionvoidaddShutdownHook(Thread hook)Registers a new virtual-machine shutdown hook.intavailableProcessors()Returns the number of processors available to the Java virtual machine.Processexec(String command)Executes the specified string command in a separate process.Processexec(String[] cmdarray)Executes the specified command and arguments in a separate process.Processexec(String[] cmdarray, String[] envp)Executes the specified command and arguments in a separate process with the specified environment.Processexec(String[] cmdarray, String[] envp, File dir)Executes the specified command and arguments in a separate process with the specified environment and working directory.Processexec(String command, String[] envp)Executes the specified string command in a separate process with the specified environment.Processexec(String command, String[] envp, File dir)Executes the specified string command in a separate process with the specified environment and working directory.voidexit(int status)Terminates the currently running Java virtual machine by initiating its shutdown sequence.longfreeMemory()Returns the amount of free memory in the Java Virtual Machine.voidgc()Runs the garbage collector.InputStreamgetLocalizedInputStream(InputStream in)Deprecated. As of JDK 1.1, the preferred way to translate a byte stream in the local encoding into a character stream in Unicode is via the InputStreamReader and BufferedReader classes.OutputStreamgetLocalizedOutputStream(OutputStream out)Deprecated. As of JDK 1.1, the preferred way to translate a Unicode character stream into a byte stream in the local encoding is via the OutputStreamWriter, BufferedWriter, and PrintWriter classes.static RuntimegetRuntime()Returns the runtime object associated with the current Java application.voidhalt(int status)Forcibly terminates the currently running Java virtual machine.voidload(String filename)Loads the native library specified by the filename argument.voidloadLibrary(String libname)Loads the native library specified by the libname argument.longmaxMemory()Returns the maximum amount of memory that the Java virtual machine will attempt to use.booleanremoveShutdownHook(Thread hook)De-registers a previously-registered virtual-machine shutdown hook.voidrunFinalization()Runs the finalization methods of any objects pending finalization.static voidrunFinalizersOnExit(boolean value)Deprecated. This method was originally designed to enable or disable running finalizers on exit. Running finalizers on exit was disabled by default. If enabled, then the finalizers of all objects whose finalizers had not yet been automatically invoked were to be run before the Java runtime exits. That behavior 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.longtotalMemory()Returns the total amount of memory in the Java virtual machine.voidtraceInstructions(boolean on)Enables/Disables tracing of instructions.voidtraceMethodCalls(boolean on)Enables/Disables tracing of method calls.Methods inherited from class java.lang.Objectclone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, waitMethod DetailgetRuntimepublic static Runtime getRuntime()Returns the runtime object associated with the current Java application. Most of the methods of class Runtime are instance methods and must be invoked with respect to the current runtime object.Returns:the Runtime object associated with the current Java application.exitpublic void exit(int status)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. All registered shutdown hooks, if any, are started in some unspecified order and allowed to run concurrently until they finish. Once this is done the virtual machine halts. If this method is invoked after all shutdown hooks have already been run and the status is nonzero then this method halts the virtual machine with the given status code. Otherwise, this method blocks indefinitely. The System.exit method is the conventional and convenient means of invoking this method.Parameters:status - Termination status. By convention, a nonzero status code indicates abnormal termination.Throws:SecurityException - If a security manager is present and its checkExit method does not permit exiting with the specified statusSee Also:SecurityException, SecurityManager.checkExit(int), addShutdownHook(java.lang.Thread), removeShutdownHook(java.lang.Thread), halt(int)addShutdownHookpublic void addShutdownHook(Thread hook)Registers a new virtual-machine shutdown hook. The Java virtual machine shuts down in response to two kinds of events: The program exits normally, when the last non-daemon thread exits or when the exit (equivalently, System.exit) method is invoked, or The virtual machine is terminated in response to a user interrupt, such as typing ^C, or a system-wide event, such as user logoff or system shutdown. A shutdown hook 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 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 exit method. Once the shutdown sequence has begun it can be stopped only by invoking the halt method, which forcibly terminates the virtual machine. 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 IllegalStateException to be thrown. 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. Shutdown hooks should also finish their work quickly. When a program invokes exit 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. Uncaught exceptions are handled in shutdown hooks just as in any other thread, by invoking the uncaughtException method of the thread's ThreadGroup object. The default implementation of this method prints the exception's stack trace to System.err and terminates the thread; it does not cause the virtual machine to exit or halt. In rare circumstances the virtual machine may abort, that is, stop running without shutting down cleanly. This occurs when the virtual machine is terminated externally, for example with the SIGKILL signal on Unix or the TerminateProcess 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.Parameters:hook - An initialized but unstarted Thread objectThrows: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 runIllegalStateException - If the virtual machine is already in the process of shutting downSecurityException - If a security manager is present and it denies RuntimePermission("shutdownHooks")Since:1.3See Also:removeShutdownHook(java.lang.Thread), halt(int), exit(int)
removeShutdownHookpublic boolean removeShutdownHook(Thread hook)De-registers a previously-registered virtual-machine shutdown hook. Parameters:hook - the hook to removeReturns:true if the specified hook had previously been registered and was successfully de-registered, false otherwise.Throws:IllegalStateException - If the virtual machine is already in the process of shutting downSecurityException - If a security manager is present and it denies RuntimePermission("shutdownHooks")Since:1.3See Also:addShutdownHook(java.lang.Thread), exit(int)haltpublic void halt(int status)Forcibly terminates the currently running Java virtual machine. This method never returns normally. This method should be used with extreme caution. Unlike the exit method, this method does not cause shutdown hooks to be started. If the shutdown sequence has already been initiated then this method does not wait for any running shutdown hooks to finish their work.Parameters:status - Termination status. By convention, a nonzero status code indicates abnormal termination. If the exit (equivalently, System.exit) 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 checkExit method does not permit an exit with the specified statusSince:1.3See Also:exit(int), addShutdownHook(java.lang.Thread), removeShutdownHook(java.lang.Thread)runFinalizersOnExit@Deprecatedpublic static void runFinalizersOnExit(boolean value)Deprecated. This method was originally designed to enable or disable running finalizers on exit. Running finalizers on exit was disabled by default. If enabled, then the finalizers of all objects whose finalizers had not yet been automatically invoked were to be run before the Java runtime exits. That behavior 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 UnsupportedOperationException.Parameters:value - ignoredSince:JDK1.1execpublic Process exec(String command) throws IOExceptionExecutes the specified string command in a separate process. This is a convenience method. An invocation of the form exec(command) behaves in exactly the same way as the invocation exec(command, null, null).Parameters:command - a specified system command.Returns:A new Process object for managing the subprocessThrows:SecurityException - If a security manager exists and its checkExec method doesn't allow creation of the subprocessIOException - If an I/O error occursNullPointerException - If command is nullIllegalArgumentException - If command is emptySee Also:exec(String[], String[], File), ProcessBuilderexecpublic Process exec(String command, String[] envp) throws IOExceptionExecutes the specified string command in a separate process with the specified environment. This is a convenience method. An invocation of the form exec(command, envp) behaves in exactly the same way as the invocation exec(command, envp, null).Parameters:command - a specified system command.envp - array of strings, each element of which has environment variable settings in the format name=value, or null if the subprocess should inherit the environment of the current process.Returns:A new Process object for managing the subprocessThrows:SecurityException - If a security manager exists and its checkExec method doesn't allow creation of the subprocessIOException - If an I/O error occursNullPointerException - If command is null, or one of the elements of envp is nullIllegalArgumentException - If command is emptySee Also:exec(String[], String[], File), ProcessBuilderexecpublic Process exec(String command, String[] envp, File dir) throws IOExceptionExecutes the specified string command in a separate process with the specified environment and working directory. This is a convenience method. An invocation of the form exec(command, envp, dir) behaves in exactly the same way as the invocation exec(cmdarray, envp, dir), where cmdarray is an array of all the tokens in command. More precisely, the command string is broken into tokens using a StringTokenizer created by the call new StringTokenizer(command) with no further modification of the character categories. The tokens produced by the tokenizer are then placed in the new string array cmdarray, in the same order.Parameters:command - a specified system command.envp - array of strings, each element of which has environment variable settings in the format name=value, or null if the subprocess should inherit the environment of the current process.dir - the working directory of the subprocess, or null if the subprocess should inherit the working directory of the current process.Returns:A new Process object for managing the subprocessThrows:SecurityException - If a security manager exists and its checkExec method doesn't allow creation of the subprocessIOException - If an I/O error occursNullPointerException - If command is null, or one of the elements of envp is nullIllegalArgumentException - If command is emptySince:1.3See Also:ProcessBuilderexecpublic Process exec(String[] cmdarray) throws IOExceptionExecutes the specified command and arguments in a separate process. This is a convenience method. An invocation of the form exec(cmdarray) behaves in exactly the same way as the invocation exec(cmdarray, null, null).Parameters:cmdarray - array containing the command to call and its arguments.Returns:A new Process object for managing the subprocessThrows:SecurityException - If a security manager exists and its checkExec method doesn't allow creation of the subprocessIOException - If an I/O error occursNullPointerException - If cmdarray is null, or one of the elements of cmdarray is nullIndexOutOfBoundsException - If cmdarray is an empty array (has length 0)See Also:ProcessBuilderexecpublic Process exec(String[] cmdarray, String[] envp) throws IOExceptionExecutes the specified command and arguments in a separate process with the specified environment. This is a convenience method. An invocation of the form exec(cmdarray, envp) behaves in exactly the same way as the invocation exec(cmdarray, envp, null).Parameters:cmdarray - array containing the command to call and its arguments.envp - array of strings, each element of which has environment variable settings in the format name=value, or null if the subprocess should inherit the environment of the current process.Returns:A new Process object for managing the subprocessThrows:SecurityException - If a security manager exists and its checkExec method doesn't allow creation of the subprocessIOException - If an I/O error occursNullPointerException - If cmdarray is null, or one of the elements of cmdarray is null, or one of the elements of envp is nullIndexOutOfBoundsException - If cmdarray is an empty array (has length 0)See Also:ProcessBuilderexecpublic Process exec(String[] cmdarray, String[] envp, File dir) throws IOExceptionExecutes the specified command and arguments in a separate process with the specified environment and working directory. Given an array of strings cmdarray, representing the tokens of a command line, and an array of strings envp, representing "environment" variable settings, this method creates a new process in which to execute the specified command. This method checks that cmdarray 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. If envp is null, the subprocess inherits the environment settings of the current process. 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. ProcessBuilder.start() is now the preferred way to start a process with a modified environment. The working directory of the new subprocess is specified by dir. If dir is null, the subprocess inherits the current working directory of the current process. If a security manager exists, its checkExec method is invoked with the first component of the array cmdarray as its argument. This may result in a SecurityException being thrown. Starting an operating system process is highly system-dependent. Among the many things that can go wrong are: The operating system program file was not found. Access to the program file was denied. The working directory does not exist. 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 IOException.Parameters:cmdarray - array containing the command to call and its arguments.envp - array of strings, each element of which has environment variable settings in the format name=value, or null if the subprocess should inherit the environment of the current process.dir - the working directory of the subprocess, or null if the subprocess should inherit the working directory of the current process.Returns:A new Process object for managing the subprocessThrows:SecurityException - If a security manager exists and its checkExec method doesn't allow creation of the subprocessIOException - If an I/O error occursNullPointerException - If cmdarray is null, or one of the elements of cmdarray is null, or one of the elements of envp is nullIndexOutOfBoundsException - If cmdarray is an empty array (has length 0)Since:1.3See Also:ProcessBuilder
availableProcessorspublic int availableProcessors()Returns the number of processors available to the Java virtual machine. 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.
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