public class Runtime extends Object
Every Java application has a single instance of class Runtime
that allows the application to interface with the environment in which the application is running. The current runtime can be obtained from the getRuntime
method.
An application cannot create its own instance of this class.
getRuntime()
public 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.
Runtime
object associated with the current Java application.public 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.
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
method is the conventional and convenient means of invoking this method. System.exit
status
- Termination status. By convention, a nonzero status code indicates abnormal termination.SecurityException
- If a security manager is present and its checkExit
method does not permit exiting with the specified statusSecurityException
, SecurityManager.checkExit(int)
, addShutdownHook(java.lang.Thread)
, removeShutdownHook(java.lang.Thread)
, runFinalizersOnExit(boolean)
, halt(int)
public void addShutdownHook(Thread hook)
Registers a new virtual-machine shutdown hook.
The Java virtual machine shuts down in response to two kinds of events:
exit
(equivalently, System.exit
) method is invoked, or ^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
method. exit
Once the shutdown sequence has begun it can be stopped only by invoking the
method, which forcibly terminates the virtual machine. halt
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
to be thrown. IllegalStateException
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
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. exit
Uncaught exceptions are handled in shutdown hooks just as in any other thread, by invoking the
method of the thread's uncaughtException
object. The default implementation of this method prints the exception's stack trace to ThreadGroup
and terminates the thread; it does not cause the virtual machine to exit or halt. System.err
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.
hook
- An initialized but unstarted Thread
objectIllegalArgumentException
- 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")
removeShutdownHook(java.lang.Thread)
, halt(int)
, exit(int)
public boolean removeShutdownHook(Thread hook)
De-registers a previously-registered virtual-machine shutdown hook.
hook
- the hook to removetrue
if the specified hook had previously been registered and was successfully de-registered, false
otherwise.IllegalStateException
- If the virtual machine is already in the process of shutting downSecurityException
- If a security manager is present and it denies RuntimePermission
("shutdownHooks")
addShutdownHook(java.lang.Thread)
, exit(int)
public 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
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. exit
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.SecurityException
- If a security manager is present and its checkExit
method does not permit an exit with the specified statusexit(int)
, addShutdownHook(java.lang.Thread)
, removeShutdownHook(java.lang.Thread)
@Deprecated public static void runFinalizersOnExit(boolean value)
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.
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.
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.
value
- true to enable finalization on exit, false to disableSecurityException
- if a security manager exists and its checkExit
method doesn't allow the exit.exit(int)
, gc()
, SecurityManager.checkExit(int)
public Process exec(String command) throws IOException
Executes 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)
command
- a specified system command.Process
object for managing the subprocessSecurityException
- 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
IllegalArgumentException
- If command
is emptyexec(String[], String[], File)
, ProcessBuilder
public Process exec(String command, String[] envp) throws IOException
Executes 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)
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.Process
object for managing the subprocessSecurityException
- 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 null
IllegalArgumentException
- If command
is emptyexec(String[], String[], File)
, ProcessBuilder
public Process exec(String command, String[] envp, File dir) throws IOException
Executes 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
, where exec
(cmdarray, envp, dir)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
with no further modification of the character categories. The tokens produced by the tokenizer are then placed in the new string array StringTokenizer
(command)cmdarray
, in the same order.
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.Process
object for managing the subprocessSecurityException
- 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 null
IllegalArgumentException
- If command
is emptyProcessBuilder
public Process exec(String[] cmdarray) throws IOException
Executes 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)
cmdarray
- array containing the command to call and its arguments.Process
object for managing the subprocessSecurityException
- 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
IndexOutOfBoundsException
- If cmdarray
is an empty array (has length 0
)ProcessBuilder
public Process exec(String[] cmdarray, String[] envp) throws IOException
Executes 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)
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.Process
object for managing the subprocessSecurityException
- 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 null
IndexOutOfBoundsException
- If cmdarray
is an empty array (has length 0
)ProcessBuilder
public Process exec(String[] cmdarray, String[] envp, File dir) throws IOException
Executes 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:
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
.
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.Process
object for managing the subprocessSecurityException
- 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 null
IndexOutOfBoundsException
- If cmdarray
is an empty array (has length 0
)ProcessBuilder
public 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.
public long freeMemory()
Returns the amount of free memory in the Java Virtual Machine. Calling the gc
method may result in increasing the value returned by freeMemory.
public long totalMemory()
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.
Note that the amount of memory required to hold an object of any given type may be implementation-dependent.
public long maxMemory()
Returns the maximum amount of memory that the Java virtual machine will attempt to use. If there is no inherent limit then the value Long.MAX_VALUE
will be returned.
public void gc()
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.
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.
public void runFinalization()
Runs the finalization methods of any objects pending finalization. Calling this method suggests that the Java virtual machine expend effort toward running the finalize
methods of objects that have been found to be discarded but whose finalize
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.
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.
Object.finalize()
public void traceInstructions(boolean on)
Enables/Disables tracing of instructions. If the boolean
argument is true
, 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.
If the boolean
argument is false
, this method causes the virtual machine to stop performing the detailed instruction trace it is performing.
on
- true
to enable instruction tracing; false
to disable this feature.public void traceMethodCalls(boolean on)
Enables/Disables tracing of method calls. If the boolean
argument is true
, 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.
Calling this method with argument false suggests that the virtual machine cease emitting per-call debugging information.
on
- true
to enable instruction tracing; false
to disable this feature.public void load(String filename)
Loads the native library specified by the filename argument. The filename argument must be an absolute path name. (for example Runtime.getRuntime().load("/home/avh/lib/libX11.so");
). 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.
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.
filename
- the file to load.SecurityException
- if a security manager exists and its checkLink
method doesn't allow loading of the specified dynamic libraryUnsatisfiedLinkError
- 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.NullPointerException
- if filename
is null
getRuntime()
, SecurityException
, SecurityManager.checkLink(java.lang.String)
public void loadLibrary(String libname)
Loads the native library specified by the libname
argument. The libname
argument must not contain any platform specific prefix, file extension or path. If a native library called libname
is statically linked with the VM, then the JNI_OnLoad_libname
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.
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:
static { System.loadLibrary("LibFile"); }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.
If this method is called more than once with the same library name, the second and subsequent calls are ignored.
libname
- the name of the library.SecurityException
- if a security manager exists and its checkLink
method doesn't allow loading of the specified dynamic libraryUnsatisfiedLinkError
- 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.NullPointerException
- if libname
is null
SecurityException
, SecurityManager.checkLink(java.lang.String)
@Deprecated public InputStream getLocalizedInputStream(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.
Creates a localized version of an input stream. This method takes an InputStream
and returns an InputStream
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.
If the argument is already a localized stream, it may be returned as the result.
in
- InputStream to localizeInputStream
, BufferedReader.BufferedReader(java.io.Reader)
, InputStreamReader.InputStreamReader(java.io.InputStream)
@Deprecated public OutputStream getLocalizedOutputStream(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.
Creates a localized version of an output stream. This method takes an OutputStream
and returns an OutputStream
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.
If the argument is already a localized stream, it may be returned as the result.
out
- OutputStream to localizeOutputStream
, BufferedWriter.BufferedWriter(java.io.Writer)
, OutputStreamWriter.OutputStreamWriter(java.io.OutputStream)
, PrintWriter.PrintWriter(java.io.OutputStream)
© 1993–2017, Oracle and/or its affiliates. All rights reserved.
Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.