java.lang

Class System

java.lang.Object

java.lang.System

public final class System
extends Object

Provides access to system-related information and resources including standard input and output. Enables clients to dynamically load native libraries. All methods of this class are accessed in a static way and the class itself can not be instantiated.

See Also:

Runtime

Field Summary

Fields

Modifier and Type	Field and Description
static PrintStream	err Default error output stream.
static InputStream	in Default input stream.
static PrintStream	out Default output stream.

Method Summary

Modifier and Type	Method and Description
static void	arraycopy(boolean[] src, int srcPos, boolean[] dst, int dstPos, int length) The boolean[] specialized version of arraycopy().
static void	arraycopy(byte[] src, int srcPos, byte[] dst, int dstPos, int length) The byte[] specialized version of arraycopy().
static void	arraycopy(char[] src, int srcPos, char[] dst, int dstPos, int length) The char[] specialized version of arraycopy().
static void	arraycopy(double[] src, int srcPos, double[] dst, int dstPos, int length) The double[] specialized version of arraycopy().
static void	arraycopy(float[] src, int srcPos, float[] dst, int dstPos, int length) The float[] specialized version of arraycopy().
static void	arraycopy(int[] src, int srcPos, int[] dst, int dstPos, int length) The int[] specialized version of arraycopy().
static void	arraycopy(long[] src, int srcPos, long[] dst, int dstPos, int length) The long[] specialized version of arraycopy().
static void	arraycopy(Object src, int srcPos, Object dst, int dstPos, int length) Copies length elements from the array src, starting at offset srcPos, into the array dst, starting at offset dstPos.
static void	arraycopy(short[] src, int srcPos, short[] dst, int dstPos, int length) The short[] specialized version of arraycopy().
static String	clearProperty(String name) Removes a specific system property.
static Console	console() Returns the Console associated with this VM, or null.
static long	currentTimeMillis() Returns the current time in milliseconds since January 1, 1970 00:00:00.0 UTC.
static void	exit(int code) Causes the VM to stop running and the program to exit with the given exit status.
static void	gc() Indicates to the VM that it would be a good time to run the garbage collector.
static Map<String,String>	getenv() Returns an unmodifiable map of all environment variables to their values.
static String	getenv(String name) Returns the value of the environment variable with the given name, or null if no such variable exists.
static Properties	getProperties() Returns the system properties.
static String	getProperty(String propertyName) Returns the value of a particular system property or null if no such property exists.
static String	getProperty(String name, String defaultValue) Returns the value of a particular system property.
static SecurityManager	getSecurityManager() Returns null.
static int	identityHashCode(Object anObject) Returns an integer hash code for the parameter.
static Channel	inheritedChannel() Returns the inherited channel from the creator of the current virtual machine.
static String	lineSeparator() Returns the system's line separator.
static void	load(String pathName) See Runtime.load(java.lang.String).
static void	loadLibrary(String libName) See Runtime.loadLibrary(java.lang.String).
static void	logE(String message)
static void	logE(String message, Throwable th)
static void	logI(String message)
static void	logI(String message, Throwable th)
static void	logW(String message)
static void	logW(String message, Throwable th)
static String	mapLibraryName(String nickname) Returns the platform specific file name format for the shared library named by the argument.
static long	nanoTime() Returns the current timestamp of the most precise timer available on the local system, in nanoseconds.
static void	runFinalization() Provides a hint to the VM that it would be useful to attempt to perform any outstanding object finalization.
static void	runFinalizersOnExit(boolean flag) Deprecated. This method is unsafe.
static void	setErr(PrintStream newErr) Sets the standard error output stream to the given user defined output stream.
static void	setIn(InputStream newIn) Sets the standard input stream to the given user defined input stream.
static void	setOut(PrintStream newOut) Sets the standard output stream to the given user defined output stream.
static void	setProperties(Properties p) Attempts to set all system properties.
static String	setProperty(String name, String value) Sets the value of a particular system property.
static void	setSecurityManager(SecurityManager sm) Throws SecurityException.
static void	setUnchangeableSystemProperty(String name, String value) Inits an unchangeable system property with the given value.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

in

public static final InputStream in

Default input stream.

out

public static final PrintStream out

Default output stream.

err

public static final PrintStream err

Default error output stream.

Method Detail

setIn

public static void setIn(InputStream newIn)

Sets the standard input stream to the given user defined input stream.

Parameters:

newIn - the user defined input stream to set as the standard input stream.

setOut

public static void setOut(PrintStream newOut)

Sets the standard output stream to the given user defined output stream.

Parameters:

newOut - the user defined output stream to set as the standard output stream.

setErr

public static void setErr(PrintStream newErr)

Sets the standard error output stream to the given user defined output stream.

Parameters:

newErr - the user defined output stream to set as the standard error output stream.

arraycopy

public static void arraycopy(Object src,
                             int srcPos,
                             Object dst,
                             int dstPos,
                             int length)

Copies length elements from the array src, starting at offset srcPos, into the array dst, starting at offset dstPos.

The source and destination arrays can be the same array, in which case copying is performed as if the source elements are first copied into a temporary array and then into the destination array.

Parameters:

src - the source array to copy the content.

srcPos - the starting index of the content in src.

dst - the destination array to copy the data into.

dstPos - the starting index for the copied content in dst.

length - the number of elements to be copied.

arraycopy

public static void arraycopy(char[] src,
                             int srcPos,
                             char[] dst,
                             int dstPos,
                             int length)

The char[] specialized version of arraycopy().

arraycopy

public static void arraycopy(byte[] src,
                             int srcPos,
                             byte[] dst,
                             int dstPos,
                             int length)

The byte[] specialized version of arraycopy().

arraycopy

public static void arraycopy(short[] src,
                             int srcPos,
                             short[] dst,
                             int dstPos,
                             int length)

The short[] specialized version of arraycopy().

arraycopy

public static void arraycopy(int[] src,
                             int srcPos,
                             int[] dst,
                             int dstPos,
                             int length)

The int[] specialized version of arraycopy().

arraycopy

public static void arraycopy(long[] src,
                             int srcPos,
                             long[] dst,
                             int dstPos,
                             int length)

The long[] specialized version of arraycopy().

arraycopy

public static void arraycopy(float[] src,
                             int srcPos,
                             float[] dst,
                             int dstPos,
                             int length)

The float[] specialized version of arraycopy().

arraycopy

public static void arraycopy(double[] src,
                             int srcPos,
                             double[] dst,
                             int dstPos,
                             int length)

The double[] specialized version of arraycopy().

arraycopy

public static void arraycopy(boolean[] src,
                             int srcPos,
                             boolean[] dst,
                             int dstPos,
                             int length)

The boolean[] specialized version of arraycopy().

currentTimeMillis

public static long currentTimeMillis()

Returns the current time in milliseconds since January 1, 1970 00:00:00.0 UTC.

This method always returns UTC times, regardless of the system's time zone. This is often called "Unix time" or "epoch time". Use a DateFormat instance to format this time for display to a human.

This method shouldn't be used for measuring timeouts or other elapsed time measurements, as changing the system time can affect the results. Use nanoTime() for that.

nanoTime

public static long nanoTime()

Returns the current timestamp of the most precise timer available on the local system, in nanoseconds. Equivalent to Linux's CLOCK_MONOTONIC.

This timestamp should only be used to measure a duration by comparing it against another timestamp on the same device. Values returned by this method do not have a defined correspondence to wall clock times; the zero value is typically whenever the device last booted. Use currentTimeMillis() if you want to know what time it is.

exit

public static void exit(int code)

Causes the VM to stop running and the program to exit with the given exit status. If runFinalizersOnExit(boolean) has been previously invoked with a true argument, then all objects will be properly garbage-collected and finalized first.

gc

public static void gc()

Indicates to the VM that it would be a good time to run the garbage collector. Note that this is a hint only. There is no guarantee that the garbage collector will actually be run.

getenv

public static String getenv(String name)

Returns the value of the environment variable with the given name, or null if no such variable exists.

getenv

public static Map<String,String> getenv()

Returns an unmodifiable map of all environment variables to their values.

inheritedChannel

public static Channel inheritedChannel()
                                throws IOException

Returns the inherited channel from the creator of the current virtual machine.

Returns:

the inherited Channel or null if none exists.

Throws:

IOException - if an I/O error occurred.

See Also:

SelectorProvider, SelectorProvider.inheritedChannel()

getProperties

public static Properties getProperties()

Returns the system properties. Note that this is not a copy, so that changes made to the returned Properties object will be reflected in subsequent calls to getProperty and getProperties.

Returns:

the system properties.

setUnchangeableSystemProperty

public static void setUnchangeableSystemProperty(String name,
                                                 String value)

Inits an unchangeable system property with the given value. This is called from native code when the environment needs to change under native bridge emulation.

getProperty

public static String getProperty(String propertyName)

Returns the value of a particular system property or null if no such property exists.

The following properties are always provided by the Dalvik VM:

Name	Meaning	Example
file.separator	File.separator	/
java.class.path	System class path	.
java.class.version	(Not useful on Android)	50.0
java.compiler	(Not useful on Android)	Empty
java.ext.dirs	(Not useful on Android)	Empty
java.home	Location of the VM on the file system	/system
java.io.tmpdir	See File.createTempFile(java.lang.String, java.lang.String)	/sdcard
java.library.path	Search path for JNI libraries	/vendor/lib:/system/lib
java.vendor	Human-readable VM vendor	The Android Project
java.vendor.url	URL for VM vendor's web site	http://www.android.com/
java.version	(Not useful on Android)	0
java.specification.version	VM libraries version	0.9
java.specification.vendor	VM libraries vendor	The Android Project
java.specification.name	VM libraries name	Dalvik Core Library
java.vm.version	VM implementation version	1.2.0
java.vm.vendor	VM implementation vendor	The Android Project
java.vm.name	VM implementation name	Dalvik
java.vm.specification.version	VM specification version	0.9
java.vm.specification.vendor	VM specification vendor	The Android Project
java.vm.specification.name	VM specification name	Dalvik Virtual Machine Specification
line.separator	The system line separator	\n
os.arch	OS architecture	armv7l
os.name	OS (kernel) name	Linux
os.version	OS (kernel) version	2.6.32.9-g103d848
path.separator	See File.pathSeparator	:
user.dir	Base of non-absolute paths	/
user.home	(Not useful on Android)	Empty
user.name	(Not useful on Android)	Empty

All of the above properties except for user.home and java.io.tmpdir cannot be modified. Any attempt to change them will be a no-op.

Parameters:

propertyName - the name of the system property to look up.

Returns:

the value of the specified system property or null if the property doesn't exist.

getProperty

public static String getProperty(String name,
                                 String defaultValue)

Returns the value of a particular system property. The defaultValue will be returned if no such property has been found.

setProperty

public static String setProperty(String name,
                                 String value)

Sets the value of a particular system property. Most system properties are read only and cannot be cleared or modified. See getProperty(java.lang.String) for a list of such properties.

Returns:

the old value of the property or null if the property didn't exist.

clearProperty

public static String clearProperty(String name)

Removes a specific system property. Most system properties are read only and cannot be cleared or modified. See getProperty(java.lang.String) for a list of such properties.

Returns:

the property value or null if the property didn't exist.

Throws:

NullPointerException - if the argument is null.

IllegalArgumentException - if the argument is empty.

console

public static Console console()

Returns the Console associated with this VM, or null. Not all VMs will have an associated console. A console is typically only available for programs run from the command line.

Since:

1.6

getSecurityManager

public static SecurityManager getSecurityManager()

Returns null. Android does not use SecurityManager. This method is only provided for source compatibility.

Returns:

null

identityHashCode

public static int identityHashCode(Object anObject)

Returns an integer hash code for the parameter. The hash code returned is the same one that would be returned by the method java.lang.Object.hashCode(), whether or not the object's class has overridden hashCode(). The hash code for null is 0.

Parameters:

anObject - the object to calculate the hash code.

Returns:

the hash code for the given object.

See Also:

Object.hashCode()

lineSeparator

public static String lineSeparator()

Returns the system's line separator. On Android, this is "\n". The value comes from the value of the line.separator system property.

On Android versions before Lollipop the line.separator system property can be modified but this method continues to return the original value. The system property cannot be modified on later versions of Android.

Since:

1.7

load

public static void load(String pathName)

See Runtime.load(java.lang.String).

loadLibrary

public static void loadLibrary(String libName)

See Runtime.loadLibrary(java.lang.String).

logE

public static void logE(String message)

logE

public static void logE(String message,
                        Throwable th)

logI

public static void logI(String message)

logI

public static void logI(String message,
                        Throwable th)

logW

public static void logW(String message)

logW

public static void logW(String message,
                        Throwable th)

runFinalization

public static void runFinalization()

Provides a hint to the VM that it would be useful to attempt to perform any outstanding object finalization.

runFinalizersOnExit

@Deprecated
public static void runFinalizersOnExit(boolean flag)

Deprecated. This method is unsafe.

Ensures that, when the VM is about to exit, all objects are finalized. Note that all finalization which occurs when the system is exiting is performed after all running threads have been terminated.

Parameters:

flag - the flag determines if finalization on exit is enabled.

setProperties

public static void setProperties(Properties p)

Attempts to set all system properties. Copies all properties from p and discards system properties that are read only and cannot be modified. See getProperty(java.lang.String) for a list of such properties.

setSecurityManager

public static void setSecurityManager(SecurityManager sm)

Throws SecurityException.

Security managers do not provide a secure environment for executing untrusted code and are unsupported on Android. Untrusted code cannot be safely isolated within a single VM on Android, so this method always throws a SecurityException.

Parameters:

sm - a security manager

Throws:

SecurityException - always

mapLibraryName

public static String mapLibraryName(String nickname)

Returns the platform specific file name format for the shared library named by the argument. On Android, this would turn "MyLibrary" into "libMyLibrary.so".