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Java Platform 1.2
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Class java.lang.Runtime

java.lang.Object
  |
  +--java.lang.Runtime

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.

Since:

JDK1.0

See Also:

getRuntime()

Method Summary

Process	exec(String command, String[] envp) Executes the specified string command in a separate process with the specified environment.
Process	exec(String command) Executes the specified string command in a separate process.
Process	exec(String[] cmdarray, String[] envp) Executes the specified command and arguments in a separate process with the specified environment.
Process	exec(String[] cmdarray) Executes the specified command and arguments in a separate process.
void	exit(int status) Terminates the currently running Java Virtual Machine.
long	freeMemory() Returns the amount of free memory in the system.
void	gc() Runs the garbage collector.
InputStream	getLocalizedInputStream(InputStream in) Deprecated. As of JDK 1.1, the preferred way translate a byte stream in the local encoding into a character stream in Unicode is via the InputStreamReader and BufferedReader classes.
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.
static Runtime	getRuntime() Returns the runtime object associated with the current Java application.
void	load(String filename) Loads the specified filename as a dynamic library.
void	loadLibrary(String libname) Loads the dynamic library with the specified library name.
void	runFinalization() 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.
long	totalMemory() Returns the total amount of memory in the Java Virtual Machine.
void	traceInstructions(boolean on) Enables/Disables tracing of instructions.
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

getRuntime

public static Runtime getRuntime()

Returns the runtime object associated with the current Java application.

Returns:

the Runtime object associated with the current Java application.

exit

public void exit(int status)

Terminates the currently running Java Virtual Machine. This method never returns normally.

If there is a security manager, its checkExit method is called with the status as its argument. This may result in a security exception.

The argument serves as a status code; by convention, a nonzero status code indicates abnormal termination.

Parameters:

status - exit status.

Throws:

SecurityException - if the current thread cannot exit with the specified status.

See Also:

SecurityException, SecurityManager.checkExit(int)

runFinalizersOnExit

public 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. By default, finalization on exit is disabled. An invocation of the runFinalizersOnExit method is permitted only if the caller is allowed to exit, and is otherwise rejected by the security manager.

See Also:

gc(), exit(int)

exec

public Process exec(String command)
             throws IOException

Executes the specified string command in a separate process.

The command argument is parsed into tokens and then executed as a command in a separate process. This method has exactly the same effect as exec(command, null).

Parameters:

command - a specified system command.

Returns:

a Process object for managing the subprocess.

Throws:

SecurityException - if the current thread cannot create a subprocess.

See Also:

exec(java.lang.String, java.lang.String[])

exec

public Process exec(String command,
                    String[] envp)
             throws IOException

Executes the specified string command in a separate process with the specified environment.

This method breaks the command string into tokens and creates a new array cmdarray containing the tokens; it then performs the call exec(cmdarray, envp).

Parameters:

command - a specified system command.

envp - array containing environment in format name=value

Returns:

a Process object for managing the subprocess.

Throws:

SecurityException - if the current thread cannot create a subprocess.

See Also:

exec(java.lang.String[], java.lang.String[])

exec

public Process exec(String[] cmdarray)
             throws IOException

Executes the specified command and arguments in a separate process.

The command specified by the tokens in cmdarray is executed as a command in a separate process. This has exactly the same effect as exec(cmdarray, null).

Parameters:

cmdarray - array containing the command to call and its arguments.

Returns:

a Process object for managing the subprocess.

Throws:

SecurityException - if the current thread cannot create a subprocess.

See Also:

exec(java.lang.String[], java.lang.String[])

exec

public Process exec(String[] cmdarray,
                    String[] envp)
             throws IOException

Executes the specified command and arguments in a separate process with the specified environment.

If there is a security manager, its checkExec method is called with the first component of the array cmdarray as its argument. This may result in a security exception.

Given an array of strings cmdarray, representing the tokens of a command line, and an array of strings envp, representing an "environment" that defines system properties, this method creates a new process in which to execute the specified command.

Parameters:

cmdarray - array containing the command to call and its arguments.

envp - array containing environment in format name=value.

Returns:

a Process object for managing the subprocess.

Throws:

SecurityException - if the current thread cannot create a subprocess.

See Also:

Process, SecurityException, SecurityManager.checkExec(java.lang.String)

freeMemory

public long freeMemory()

Returns the amount of free memory in the system. The value returned by this method is always less than the value returned by the totalMemory method. Calling the gc method may result in increasing the value returned by freeMemory.

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.

Returns:

the total amount of memory currently available for allocating objects, measured in bytes.

gc

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 Java Virtual Machine has made its best effort to recycle all unused objects.

The name gc stands for "garbage collector". The Java Virtual Machine performs this recycling process automatically as needed even if the gc method is not invoked explicitly.

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 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 Java Virtual Machine has made a best effort to complete all outstanding finalizations.

The Java Virtual Machine performs the finalization process automatically as needed if the runFinalization method is not invoked explicitly.

See Also:

Object.finalize()

traceInstructions

public void traceInstructions(boolean on)

Enables/Disables tracing of instructions. If the boolean argument is true, this method asks the Java Virtual Machine to print out a detailed trace of each instruction in the Java Virtual Machine as it is executed. 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 Java Virtual Machine to stop performing the detailed instruction trace it is performing.

Parameters:

on - true to enable instruction tracing; false to disable this feature.

traceMethodCalls

public void traceMethodCalls(boolean on)

Enables/Disables tracing of method calls. If the boolean argument is true, this method asks the Java Virtual Machine to print out a detailed trace of each method in the Java Virtual Machine as it is called. 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 Java Virtual Machine to stop performing the detailed method trace it is performing.

Parameters:

on - true to enable instruction tracing; false to disable this feature.

load

public void load(String filename)

Loads the specified filename as a dynamic library. The filename argument must be a complete pathname. From java_g it will automagically insert "_g" before the ".so" (for example Runtime.getRuntime().load("/home/avh/lib/libX11.so");).

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

Parameters:

filename - the file to load.

Throws:

SecurityException - if the current thread cannot load the specified dynamic library.

UnsatisfiedLinkError - if the file does not exist.

See Also:

getRuntime(), SecurityException, SecurityManager.checkLink(java.lang.String)

loadLibrary

public void loadLibrary(String libname)

Loads the dynamic library with the specified library name. The mapping from a library name to a specific filename is done in a system-specific 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.

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 the current thread cannot load the specified dynamic library.

UnsatisfiedLinkError - if the library does not exist.

See Also:

SecurityException, SecurityManager.checkLink(java.lang.String)

getLocalizedInputStream

public InputStream getLocalizedInputStream(InputStream in)

Deprecated. As of JDK 1.1, the preferred way 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.

Returns:

a localized input stream.

See Also:

InputStream, BufferedReader.BufferedReader(java.io.Reader), InputStreamReader.InputStreamReader(java.io.InputStream)

getLocalizedOutputStream

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.

Returns:

a localized output stream.

See Also:

OutputStream, BufferedWriter.BufferedWriter(java.io.Writer), OutputStreamWriter.OutputStreamWriter(java.io.OutputStream), PrintWriter.PrintWriter(java.io.OutputStream)