| |||||
PREV CLASS NEXT CLASS | FRAMES NO FRAMES | ||||
SUMMARY: NESTED | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD |
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.
Method Summary | |
---|---|
void |
addShutdownHook(Thread hook) Registers a new virtual-machine shutdown hook. |
native int |
Returns the number of processors available to the Java virtual machine. |
Process |
Executes the specified string command in a separate process. |
Process |
Executes the specified string command in a separate process with the specified environment. |
Process |
Executes the specified string command in a separate process with the specified environment and working directory. |
Process |
Executes the specified command and arguments in a separate process. |
Process |
Executes the specified command and arguments in a separate process with the specified environment. |
Process |
Executes the specified command and arguments 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. |
native long |
Returns the amount of free memory in the Java Virtual Machine. |
native void |
gc() Runs the garbage collector. |
InputStream |
Creates a localized version of an input stream. |
OutputStream |
Creates a localized version of an output stream. |
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 specified filename as a dynamic library. |
void |
loadLibrary(String libname) Loads the dynamic library with the specified library name. |
native 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. |
static void |
runFinalizersOnExit(boolean value) 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. |
native long |
Returns the total amount of memory in the Java virtual machine. |
native void |
traceInstructions(boolean on) Enables/Disables tracing of instructions. |
native void |
traceMethodCalls(boolean on) Enables/Disables tracing of method calls. |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Method Detail |
---|
public void addShutdownHook(Thread hook)
The Java virtual machine shuts down in response to two kinds of events:
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 {@link #exit exit} method.
Once the shutdown sequence has begun it can be stopped only by invoking the {@link #halt 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 {@link 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 {@link #exit 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 {@link ThreadGroup#uncaughtException uncaughtException} method of the thread's {@link ThreadGroup} object. The default implementation of this method prints the exception's stack trace to {@link 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.
hook
- An initialized but unstarted {@link Thread} objectpublic native int 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.
public Process exec(String command) throws IOException
This is a convenience method. An invocation of the form exec(command) behaves in exactly the same way as the invocation {@link #exec(String, String[], File) exec}(command, null, null).
command
- a specified system command.IOException
- If an I/O error occurspublic Process exec(String command, String[] envp) throws IOException
This is a convenience method. An invocation of the form exec(command, envp) behaves in exactly the same way as the invocation {@link #exec(String, String[], File) 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.IOException
- If an I/O error occurspublic Process exec(String command, String[] envp, File dir) throws IOException
This is a convenience method. An invocation of the form
exec(command, envp, dir)
behaves in exactly the same way as the invocation
{@link #exec(String[], String[], File) 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 {@link StringTokenizer} created by the call
new {@link 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.
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.IOException
- If an I/O error occurspublic Process exec(String[] cmdarray) throws IOException
This is a convenience method. An invocation of the form exec(cmdarray) behaves in exactly the same way as the invocation {@link #exec(String[], String[], File) exec}(cmdarray, null, null).
cmdarray
- array containing the command to call and
its arguments.IOException
- If an I/O error occurspublic Process exec(String[] cmdarray, String[] envp) throws IOException
This is a convenience method. An invocation of the form exec(cmdarray, envp) behaves in exactly the same way as the invocation {@link #exec(String[], String[], File) 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.IOException
- If an I/O error occurspublic Process exec(String[] cmdarray, String[] envp, File dir) throws IOException
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.
{@link 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
{@link SecurityManager#checkExec checkExec}
method is invoked with the first component of the array
cmdarray
as its argument. This may result in a
{@link 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 {@link 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.IOException
- If an I/O error occurspublic void exit(int status)
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}.
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 {@link System#exit(int) System.exit} method is the conventional and convenient means of invoking this method.
status
- Termination status. By convention, a nonzero status code
indicates abnormal termination.public native long freeMemory()
gc
method may result in increasing the value returned
by freeMemory.
public native void gc()
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 {@link System#gc()} is the conventional and convenient means of invoking this method.
public InputStream getLocalizedInputStream(InputStream in)
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 localizepublic OutputStream getLocalizedOutputStream(OutputStream out)
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 localizepublic static Runtime getRuntime()
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 halt(int status)
This method should be used with extreme caution. Unlike the {@link #exit 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.
status
- Termination status. By convention, a nonzero status code
indicates abnormal termination. If the {@link Runtime#exit
exit} (equivalently, {@link System#exit(int)
System.exit}) method has already been invoked then this
status code will override the status code passed to that method.public void load(String filename)
Runtime.getRuntime().load("/home/avh/lib/libX11.so");
).
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 {@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.
The method {@link System#load(String)} is the conventional and convenient means of invoking this method.
filename
- the file to load.public void loadLibrary(String libname)
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 {@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
LibFile
) 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.
libname
- the name of the library.public native long maxMemory()
public boolean removeShutdownHook(Thread hook)
hook
- the hook to removepublic void runFinalization()
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 {@link System#runFinalization()} is the conventional and convenient means of invoking this method.
public static void runFinalizersOnExit(boolean value)
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 disablepublic native long totalMemory()
Note that the amount of memory required to hold an object of any given type may be implementation-dependent.
public native void traceInstructions(boolean on)
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 native void traceMethodCalls(boolean on)
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.
| |||||
PREV CLASS NEXT CLASS | FRAMES NO FRAMES | ||||
SUMMARY: NESTED | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD |