Package java.lang

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Class Runtime

public  class  java.lang.Runtime
    extends  java.lang.Object  
{
        // Methods
    public Process exec(String  command);	
    public Process exec(String  command, String  envp[]);	
    public Process exec(String  cmdarray[]);	
    public Process exec(String  cmdarray[], String  envp[]);	
    public void exit(int  status);	
    public long freeMemory();	
    public void gc();	
    public InputStream getLocalizedInputStream(InputStream in);  
    public OutputStream getLocalizedOutputStream(OutputStream out); 
    public static Runtime getRuntime();	
    public void load(String  filename);	
    public void loadLibrary(String  libname);	
    public void runFinalization();	
    public long totalMemory();	
    public void traceInstructions(boolean  on);	
    public void traceMethodCalls(boolean  on);	
}

Every Java application has a single instance of class Runtime which 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.

Methods

exec

public Process exec(String  command) 

throws IOException 

Executes the 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) .

Return Value:

Returns a Process object for managing the subprocess.

Parameter	Description
command	a specified system command

Throw:

SecurityException

If the current thread cannot create a subprocess.

exec

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

throws IOException 

Executes the 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) .

Return Value:

Returns a Process object for managing the subprocess.

Parameter	Description
command	a specified system command
envp	array containing environment in format name=value

Throw:

SecurityException

If the current thread cannot create a subprocess.

exec

public Process exec(String  cmdarray[]) 

throws IOException 

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

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) .

Return Value:

Returns a Process object for managing the subprocess.

Parameter	Description
cmdarray	array containing the command to call and its arguments

Throw:

SecurityException

If the current thread cannot create a subprocess.

exec

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

throws IOException 

Executes the command in a separate process with the specified arguments and 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,

Return Value:

Returns a Process object for managing the subprocess.

Parameter	Description
cmdarray	array containing the command to call and its arguments
envp	array containing environment in format name=value

Throw:

SecurityException

If the current thread cannot create a subprocess.

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.

Parameter	Description
status	exit status

Throw:

SecurityException

If the current thread cannot exit with the specified status.

freeMemory

public long freeMemory() 

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

Return Value:

Returns an approximation to the total amount of memory currently available for future allocated objects, measured in bytes, is returned. .

gc

public void gc() 

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.

getLocalizedInputStream

public InputStream getLocalizedInputStream(InputStream  in) 

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.

Return Value:

Returns a localized input stream.

getLocalizedOutputStream

public OutputStream getLocalizedOutputStream(OutputStream  out) 

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.

Return Value:

Returns a localized output stream.

getRuntime

public static Runtime getRuntime() 

Return Value:

Returns the Runtime object associated with the current Java application.

load

public  void load(String  filename) 

Loads the given filename as a dynamic library. The filename argument must be a complete path name.

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

Parameter	Description
filename	the file to load

Throw:

UnsatisfiedLinkError

If the file does not exist.

Throw:

SecurityException

If the current thread cannot load the specified dynamic library.

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 is 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 an security exception .

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

Parameter	Description
libname	the name of the library

Throw:

UnsatisfiedLinkError

If the library does not exist.

Throw:

SecurityException

If the current thread cannot load the specified dynamic library.

runFinalization

public void runFinalization() 

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.

totalMemory

public long totalMemory() 

Determines the total amount of memory in the Java Virtual Machine.

Return Value:

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

traceInstructions

public void traceInstructions(boolean  on) 

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 a detailed instruction trace it is performing.

Parameter	Description
on	true to enable instruction tracing; false to disable this feature

traceMethodCalls

public void traceMethodCalls(boolean  on) 

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 a detailed method trace it is performing.

Parameter	Description
on	true to enable instruction tracing; false to disable this feature