Runtime getruntime exec android

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Method Summary

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Modifier and Type	Method and Description
void	addShutdownHook (Thread hook)

Methods inherited from class java.lang.Object

Method Detail

getRuntime

The virtual machine’s shutdown sequence consists of two phases. In the first phase all registered 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 halts .

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.

The System.exit method is the conventional and convenient means of invoking this method.

addShutdownHook

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 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 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.

removeShutdownHook

This method should be used with extreme caution. Unlike the exit 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.

runFinalizersOnExit

If there is a security manager, its checkExit method is first called with 0 as its argument to ensure the exit is allowed. This could result in a SecurityException.

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).

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).

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.

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).

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).

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 .

availableProcessors

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.

freeMemory

totalMemory

Note that the amount of memory required to hold an object of any given type may be implementation-dependent.

maxMemory

The name gc stands for «garbage collector». The virtual machine performs this recycling process automatically as needed, in a separate thread, even if the gc method is not invoked explicitly.

The method System.gc() is the conventional and convenient means of invoking this method.

runFinalization

The virtual machine performs the finalization process automatically as needed, in a separate thread, if the runFinalization method is not invoked explicitly.

The method System.runFinalization() is the conventional and convenient means of invoking this method.

traceInstructions

If the boolean argument is false , this method causes the virtual machine to stop performing the detailed instruction trace it is performing.

traceMethodCalls

Calling this method with argument false suggests that the virtual machine cease emitting per-call debugging information.

First, if there is a security manager, its checkLink method is called with the filename as its argument. This may result in a security exception.

This is similar to the method 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.

The method System.load(String) is the conventional and convenient means of invoking this method.

loadLibrary

First, if there is a security manager, its checkLink method is called with the libname as its argument. This may result in a security exception.

The method 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 LibFile ) and then to put a static initializer:

If this method is called more than once with the same library name, the second and subsequent calls are ignored.

getLocalizedInputStream

If the argument is already a localized stream, it may be returned as the result.

getLocalizedOutputStream

If the argument is already a localized stream, it may be returned as the result.

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