public class Runtime extends Object
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.
- Since:
- 1.0
- See Also:
getRuntime()
-
Nested Class Summary
Modifier and TypeClassDescriptionstatic class
A representation of a version string for an implementation of the Java SE Platform. -
Method Summary
Modifier and TypeMethodDescriptionvoid
addShutdownHook(Thread hook)
Registers a new virtual-machine shutdown hook.int
Returns the number of processors available to the Java virtual machine.Executes the specified string command in a separate process.Executes the specified command and arguments in a separate process.Executes the specified command and arguments in a separate process with the specified environment.Executes the specified command and arguments in a separate process with the specified environment and working directory.Executes the specified string command in a separate process with the specified environment.Executes the specified string command in a separate process with the specified environment and working directory.void
exit(int status)
Terminates the currently running Java virtual machine by initiating its shutdown sequence.long
Returns the amount of free memory in the Java Virtual Machine.void
gc()
Runs the garbage collector in the Java Virtual Machine.static Runtime
Returns the runtime object associated with the current Java application.void
halt(int status)
Forcibly terminates the currently running Java virtual machine.void
Loads the native library specified by the filename argument.void
loadLibrary(String libname)
Loads the native library specified by thelibname
argument.long
Returns the maximum amount of memory that the Java virtual machine will attempt to use.boolean
removeShutdownHook(Thread hook)
De-registers a previously-registered virtual-machine shutdown hook.void
Runs the finalization methods of any objects pending finalization.long
Returns the total amount of memory in the Java virtual machine.static Runtime.Version
version()
Returns the version of the Java Runtime Environment as aRuntime.Version
.
-
Method Details
-
getRuntime
Returns the runtime object associated with the current Java application. Most of the methods of classRuntime
are instance methods and must be invoked with respect to the current runtime object.- Returns:
- the
Runtime
object associated with the current Java application.
-
exit
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.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 itscheckExit
method does not permit exiting with the specified status- See Also:
SecurityException
,SecurityManager.checkExit(int)
,addShutdownHook(java.lang.Thread)
,removeShutdownHook(java.lang.Thread)
,halt(int)
-
addShutdownHook
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'sThreadGroup
object. The default implementation of this method prints the exception's stack trace toSystem.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 theTerminateProcess
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 unstartedThread
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 runIllegalStateException
- If the virtual machine is already in the process of shutting downSecurityException
- If a security manager is present and it deniesRuntimePermission
("shutdownHooks")- Since:
- 1.3
- See Also:
removeShutdownHook(java.lang.Thread)
,halt(int)
,exit(int)
- The program exits normally, when the last non-daemon
thread exits or when the
-
removeShutdownHook
De-registers a previously-registered virtual-machine shutdown hook.- Parameters:
hook
- the hook to remove- Returns:
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 deniesRuntimePermission
("shutdownHooks")- Since:
- 1.3
- See Also:
addShutdownHook(java.lang.Thread)
,exit(int)
-
halt
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
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 theexit
(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 itscheckExit
method does not permit an exit with the specified status- Since:
- 1.3
- See Also:
exit(int)
,addShutdownHook(java.lang.Thread)
,removeShutdownHook(java.lang.Thread)
-
exec
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 invocationexec
(command, null, null)
.- Parameters:
command
- a specified system command.- Returns:
- A new
Process
object for managing the subprocess - Throws:
SecurityException
- If a security manager exists and itscheckExec
method doesn't allow creation of the subprocessIOException
- If an I/O error occursNullPointerException
- Ifcommand
isnull
IllegalArgumentException
- Ifcommand
is empty- See Also:
exec(String[], String[], File)
,ProcessBuilder
-
exec
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 invocationexec
(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, ornull
if the subprocess should inherit the environment of the current process.- Returns:
- A new
Process
object for managing the subprocess - Throws:
SecurityException
- If a security manager exists and itscheckExec
method doesn't allow creation of the subprocessIOException
- If an I/O error occursNullPointerException
- Ifcommand
isnull
, or one of the elements ofenvp
isnull
IllegalArgumentException
- Ifcommand
is empty- See Also:
exec(String[], String[], File)
,ProcessBuilder
-
exec
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 invocationexec
(cmdarray, envp, dir)
, wherecmdarray
is an array of all the tokens incommand
.More precisely, the
command
string is broken into tokens using aStringTokenizer
created by the callnew {@link StringTokenizer}(command)
with no further modification of the character categories. The tokens produced by the tokenizer are then placed in the new string arraycmdarray
, 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, ornull
if the subprocess should inherit the environment of the current process.dir
- the working directory of the subprocess, ornull
if the subprocess should inherit the working directory of the current process.- Returns:
- A new
Process
object for managing the subprocess - Throws:
SecurityException
- If a security manager exists and itscheckExec
method doesn't allow creation of the subprocessIOException
- If an I/O error occursNullPointerException
- Ifcommand
isnull
, or one of the elements ofenvp
isnull
IllegalArgumentException
- Ifcommand
is empty- Since:
- 1.3
- See Also:
ProcessBuilder
-
exec
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 invocationexec
(cmdarray, null, null)
.- Parameters:
cmdarray
- array containing the command to call and its arguments.- Returns:
- A new
Process
object for managing the subprocess - Throws:
SecurityException
- If a security manager exists and itscheckExec
method doesn't allow creation of the subprocessIOException
- If an I/O error occursNullPointerException
- Ifcmdarray
isnull
, or one of the elements ofcmdarray
isnull
IndexOutOfBoundsException
- Ifcmdarray
is an empty array (has length0
)- See Also:
ProcessBuilder
-
exec
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 invocationexec
(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, ornull
if the subprocess should inherit the environment of the current process.- Returns:
- A new
Process
object for managing the subprocess - Throws:
SecurityException
- If a security manager exists and itscheckExec
method doesn't allow creation of the subprocessIOException
- If an I/O error occursNullPointerException
- Ifcmdarray
isnull
, or one of the elements ofcmdarray
isnull
, or one of the elements ofenvp
isnull
IndexOutOfBoundsException
- Ifcmdarray
is an empty array (has length0
)- See Also:
ProcessBuilder
-
exec
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 stringsenvp
, 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
isnull
, 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
. Ifdir
isnull
, 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 arraycmdarray
as its argument. This may result in aSecurityException
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
.If the operating system does not support the creation of processes, an
UnsupportedOperationException
will be thrown.- 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, ornull
if the subprocess should inherit the environment of the current process.dir
- the working directory of the subprocess, ornull
if the subprocess should inherit the working directory of the current process.- Returns:
- A new
Process
object for managing the subprocess - Throws:
SecurityException
- If a security manager exists and itscheckExec
method doesn't allow creation of the subprocessUnsupportedOperationException
- If the operating system does not support the creation of processes.IOException
- If an I/O error occursNullPointerException
- Ifcmdarray
isnull
, or one of the elements ofcmdarray
isnull
, or one of the elements ofenvp
isnull
IndexOutOfBoundsException
- Ifcmdarray
is an empty array (has length0
)- Since:
- 1.3
- See Also:
ProcessBuilder
-
availableProcessors
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.
- Returns:
- the maximum number of processors available to the virtual machine; never smaller than one
- Since:
- 1.4
-
freeMemory
public long freeMemory()Returns the amount of free memory in the Java Virtual Machine. Calling thegc
method may result in increasing the value returned byfreeMemory.
- Returns:
- an approximation to the total amount of memory currently available for future allocated objects, measured in bytes.
-
totalMemory
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.
- Returns:
- the total amount of memory currently available for current and future objects, measured in bytes.
-
maxMemory
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 valueLong.MAX_VALUE
will be returned.- Returns:
- the maximum amount of memory that the virtual machine will attempt to use, measured in bytes
- Since:
- 1.4
-
gc
public void gc()Runs the garbage collector in the Java Virtual Machine.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 reuse by the Java Virtual Machine. When control returns from the method call, the Java Virtual Machine has made a best effort to reclaim space from all unused objects. There is no guarantee that this effort will recycle any particular number of unused objects, reclaim any particular amount of space, or complete at any particular time, if at all, before the method returns or ever.
The name
gc
stands for "garbage collector". The Java Virtual Machine performs this recycling process automatically as needed, in a separate thread, even if thegc
method is not invoked explicitly.The method
System.gc()
is the conventional and convenient means of invoking this method. -
runFinalization
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 thefinalize
methods of objects that have been found to be discarded but whosefinalize
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.- See Also:
Object.finalize()
-
load
Loads the native library specified by the filename argument. The filename argument must be an absolute path name. (for exampleRuntime.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 thefilename
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.- Parameters:
filename
- the file to load.- Throws:
SecurityException
- if a security manager exists and itscheckLink
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
- iffilename
isnull
- See Also:
getRuntime()
,SecurityException
,SecurityManager.checkLink(java.lang.String)
-
loadLibrary
Loads the native library specified by thelibname
argument. Thelibname
argument must not contain any platform specific prefix, file extension or path. If a native library calledlibname
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 thelibname
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 itLibFile
) and then to put a static initializer:
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.static { System.loadLibrary("LibFile"); }
If this method is called more than once with the same library name, the second and subsequent calls are ignored.
- Parameters:
libname
- the name of the library.- Throws:
SecurityException
- if a security manager exists and itscheckLink
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
- iflibname
isnull
- See Also:
SecurityException
,SecurityManager.checkLink(java.lang.String)
-
version
Returns the version of the Java Runtime Environment as aRuntime.Version
.- Returns:
- the
Runtime.Version
of the Java Runtime Environment - Since:
- 9
-