Added in API level 1

Summary: Fields | Methods | Inherited Methods

System

public final class System
extends Object

java.lang.Object
↳	java.lang.System

The System class contains several useful class fields and methods. It cannot be instantiated.

Among the facilities provided by the System class are standard input, standard output, and error output streams; access to externally defined properties and environment variables; a means of loading files and libraries; and a utility method for quickly copying a portion of an array.

Summary

Fields
`public static final PrintStream`	`err` The "standard" error output stream.
`public static final InputStream`	`in` The "standard" input stream.
`public static final PrintStream`	`out` The "standard" output stream.

Public methods
`static void`	`arraycopy(Object src, int srcPos, Object dest, int destPos, int length)` Copies an array from the specified source array, beginning at the specified position, to the specified position of the destination array.
`static String`	`clearProperty(String key)` Removes the system property indicated by the specified key.
`static Console`	`console()` Returns the unique `Console` object associated with the current Java virtual machine, if any.
`static long`	`currentTimeMillis()` Returns the current time in milliseconds.
`static void`	`exit(int status)` Terminates the currently running Java Virtual Machine.
`static void`	`gc()` Runs the garbage collector.
`static Properties`	`getProperties()` Determines the current system properties.
`static String`	`getProperty(String key, String def)` Gets the system property indicated by the specified key.
`static String`	`getProperty(String key)` Gets the system property indicated by the specified key.
`static SecurityManager`	`getSecurityManager()` Always returns `null` in Android
`static String`	`getenv(String name)` Gets the value of the specified environment variable.
`static Map<String, String>`	`getenv()` Returns an unmodifiable string map view of the current system environment.
`static int`	`identityHashCode(Object x)` Returns the same hash code for the given object as would be returned by the default method hashCode(), whether or not the given object's class overrides hashCode().
`static Channel`	`inheritedChannel()` Returns the channel inherited from the entity that created this Java virtual machine.
`static String`	`lineSeparator()` Returns the system-dependent line separator string.
`static void`	`load(String filename)` Loads the native library specified by the filename argument.
`static void`	`loadLibrary(String libname)` Loads the native library specified by the `libname` argument.
`static String`	`mapLibraryName(String libname)` Maps a library name into a platform-specific string representing a native library.
`static long`	`nanoTime()` Returns the current value of the running Java Virtual Machine's high-resolution time source, in nanoseconds.
`static void`	`runFinalization()` Runs the finalization methods of any objects pending finalization.
`static void`	`runFinalizersOnExit(boolean value)` This method was deprecated in API level 15. This method is inherently unsafe. It may result in finalizers being called on live objects while other threads are concurrently manipulating those objects, resulting in erratic behavior or deadlock.
`static void`	`setErr(PrintStream err)` Reassigns the "standard" error output stream.
`static void`	`setIn(InputStream in)` Reassigns the "standard" input stream.
`static void`	`setOut(PrintStream out)` Reassigns the "standard" output stream.
`static void`	`setProperties(Properties props)` Attempts to set all system properties.
`static String`	`setProperty(String key, String value)` Sets the system property indicated by the specified key.
`static void`	`setSecurityManager(SecurityManager s)` Throws `SecurityException` (except in case `sm == null`).

Inherited methods

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long timeoutMillis, int nanos)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait()` Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

Fields

err

Added in API level 1

public static final PrintStream err

The "standard" error output stream. This stream is already open and ready to accept output data.

Typically this stream corresponds to display output or another output destination specified by the host environment or user. By convention, this output stream is used to display error messages or other information that should come to the immediate attention of a user even if the principal output stream, the value of the variable out, has been redirected to a file or other destination that is typically not continuously monitored.

in

Added in API level 1

public static final InputStream in

The "standard" input stream. This stream is already open and ready to supply input data. Typically this stream corresponds to keyboard input or another input source specified by the host environment or user.

out

Added in API level 1

public static final PrintStream out

The "standard" output stream. This stream is already open and ready to accept output data. Typically this stream corresponds to display output or another output destination specified by the host environment or user.

For simple stand-alone Java applications, a typical way to write a line of output data is:

     System.out.println(data)

See the println methods in class PrintStream.

See also:

Public methods

arraycopy

Added in API level 1

public static void arraycopy (Object src, 
                int srcPos, 
                Object dest, 
                int destPos, 
                int length)

Copies an array from the specified source array, beginning at the specified position, to the specified position of the destination array. A subsequence of array components are copied from the source array referenced by src to the destination array referenced by dest. The number of components copied is equal to the length argument. The components at positions srcPos through srcPos+length-1 in the source array are copied into positions destPos through destPos+length-1, respectively, of the destination array.

If the src and dest arguments refer to the same array object, then the copying is performed as if the components at positions srcPos through srcPos+length-1 were first copied to a temporary array with length components and then the contents of the temporary array were copied into positions destPos through destPos+length-1 of the destination array.

If dest is null, then a NullPointerException is thrown.

If src is null, then a NullPointerException is thrown and the destination array is not modified.

Otherwise, if any of the following is true, an ArrayStoreException is thrown and the destination is not modified:

The src argument refers to an object that is not an array.
The dest argument refers to an object that is not an array.
The src argument and dest argument refer to arrays whose component types are different primitive types.
The src argument refers to an array with a primitive component type and the dest argument refers to an array with a reference component type.
The src argument refers to an array with a reference component type and the dest argument refers to an array with a primitive component type.

Otherwise, if any of the following is true, an IndexOutOfBoundsException is thrown and the destination is not modified:

The srcPos argument is negative.
The destPos argument is negative.
The length argument is negative.
srcPos+length is greater than src.length, the length of the source array.
destPos+length is greater than dest.length, the length of the destination array.

Otherwise, if any actual component of the source array from position srcPos through srcPos+length-1 cannot be converted to the component type of the destination array by assignment conversion, an ArrayStoreException is thrown. In this case, let k be the smallest nonnegative integer less than length such that src[srcPos+k] cannot be converted to the component type of the destination array; when the exception is thrown, source array components from positions srcPos through srcPos+k-1 will already have been copied to destination array positions destPos through destPos+k-1 and no other positions of the destination array will have been modified. (Because of the restrictions already itemized, this paragraph effectively applies only to the situation where both arrays have component types that are reference types.)

Parameters
`src`	`Object`: the source array.
`srcPos`	`int`: starting position in the source array.
`dest`	`Object`: the destination array.
`destPos`	`int`: starting position in the destination data.
`length`	`int`: the number of array elements to be copied.

Throws
`IndexOutOfBoundsException`	if copying would cause access of data outside array bounds.
`ArrayStoreException`	if an element in the `src` array could not be stored into the `dest` array because of a type mismatch.
`NullPointerException`	if either `src` or `dest` is `null`.

clearProperty

Added in API level 1

public static String clearProperty (String key)

Removes the system property indicated by the specified key.

First, if a security manager exists, its SecurityManager.checkPermission method is called with a PropertyPermission(key, "write") permission. This may result in a SecurityException being thrown. If no exception is thrown, the specified property is removed.

Parameters
`key`	`String`: the name of the system property to be removed.

Returns
`String`	the previous string value of the system property, or `null` if there was no property with that key.

Throws
`SecurityException`	if a security manager exists and its `checkPropertyAccess` method doesn't allow access to the specified system property.
`NullPointerException`	if `key` is `null`.
`IllegalArgumentException`	if `key` is empty.

See also:

console

Added in API level 9

public static Console console ()

Returns the unique Console object associated with the current Java virtual machine, if any.

Returns
`Console`	The system console, if any, otherwise `null`.

currentTimeMillis

Added in API level 1

public static long currentTimeMillis ()

Returns the current time in milliseconds. Note that while the unit of time of the return value is a millisecond, the granularity of the value depends on the underlying operating system and may be larger. For example, many operating systems measure time in units of tens of milliseconds.

See the description of the class Date for a discussion of slight discrepancies that may arise between "computer time" and coordinated universal time (UTC).

Returns
`long`	the difference, measured in milliseconds, between the current time and midnight, January 1, 1970 UTC.

See also:

Date

exit

Added in API level 1

public static void exit (int status)

Terminates the currently running Java Virtual Machine. The argument serves as a status code; by convention, a nonzero status code indicates abnormal termination.

This method calls the exit method in class Runtime. This method never returns normally.

The call System.exit(n) is effectively equivalent to the call:

 Runtime.getRuntime().exit(n)

Parameters
`status`	`int`: exit status.

Throws
`SecurityException`	if a security manager exists and its `checkExit` method doesn't allow exit with the specified status.

See also:

Runtime.exit(int)

gc

Added in API level 1

public static void gc ()

Runs the garbage collector.

Calling the gc 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 a best effort to reclaim space from all discarded objects.

The call System.gc() is effectively equivalent to the call:

 Runtime.getRuntime().gc()

At API level 34 and lower, this does nothing unless it is preceded or followed by a runFinalization call. Runtime.getRuntime().gc() always attempts to reclaim space.

Calling this indiscriminately is likely to severely degrade performance. Intended primarily for testing.

See also:

Runtime.gc()

getProperties

Added in API level 1

public static Properties getProperties ()

Determines the current system properties.

The following properties are always provided by the Dalvik VM:

Name

file.separator

java.class.path

java.class.version

java.compiler

java.ext.dirs

java.home

java.io.tmpdir

java.library.path

java.vendor

java.vendor.url

java.version

java.specification.version

java.specification.vendor

java.specification.name

java.vm.version

java.vm.vendor

java.vm.name

java.vm.specificati

java.vm.specification.name

line.separator

os.arch

os.name

os.version

path.separator

user.dir

user.home

user.name

Multiple paths in separator character of the platform.

Note that even if CLASS="TableHeadingColor"> Meaning Example File.separator / System class path . (Not useful on Android) 50.0 (Not useful on Android) Empty (Not useful on Android) Empty Location of the VM on the file system /apex/com.android.art/ Location of a temporary directory. The location varies by application. See File.createTempFile(String, String) /data/user/0/com.android.app/cache Search path for JNI libraries /vendor/lib:/system/lib Human-readable VM vendor The Android Project URL for VM vendor's web site http://www.android.com/ (Not useful on Android) 0 VM libraries version 0.9 VM libraries vendor The Android Project VM libraries name Dalvik Core Library VM implementation version 1.2.0 VM implementation vendor The Android Project VM implementation name Dalvik on.version VM specification version 0.9 on.vendor VM specification vendor The Android Project VM specification name Dalvik Virtual Machine Specification The system line separator \n OS architecture aarch64 OS (kernel) name Linux OS (kernel) version 5.10.98-g6ea688a79989 See File.pathSeparator : Base of non-absolute paths / (Not useful on Android) Empty (Not useful on Android) Empty a system property value are separated by the path the security manager does not permit the dir="ltr">getProperties operation, it may choose to permit the dir="ltr">getProperty(java.lang.String) operation.

Returns
`Properties`	the system properties

Throws
`SecurityException`	if a security manager exists and its `checkPropertiesAccess` method doesn't allow access to the system properties.

See also:

getProperty

Added in API level 1

public static String getProperty (String key, 
                String def)

Gets the system property indicated by the specified key.

First, if there is a security manager, its checkPropertyAccess method is called with the key as its argument.

If there is no current set of system properties, a set of system properties is first created and initialized in the same manner as for the getProperties method.

Parameters
`key`	`String`: the name of the system property.
`def`	`String`: a default value.

Returns
`String`	the string value of the system property, or the default value if there is no property with that key.

Throws
`SecurityException`	if a security manager exists and its `checkPropertyAccess` method doesn't allow access to the specified system property.
`NullPointerException`	if `key` is `null`.
`IllegalArgumentException`	if `key` is empty.

See also:

getProperty

Added in API level 1

public static String getProperty (String key)

Gets the system property indicated by the specified key.

First, if there is a security manager, its checkPropertyAccess method is called with the key as its argument. This may result in a SecurityException.

If there is no current set of system properties, a set of system properties is first created and initialized in the same manner as for the getProperties method.

Parameters
`key`	`String`: the name of the system property.

Returns
`String`	the string value of the system property, or `null` if there is no property with that key.

Throws
`SecurityException`	if a security manager exists and its `checkPropertyAccess` method doesn't allow access to the specified system property.
`NullPointerException`	if `key` is `null`.
`IllegalArgumentException`	if `key` is empty.

See also:

getSecurityManager

Added in API level 1

public static SecurityManager getSecurityManager ()

Always returns null in Android

Returns
`SecurityManager`	`null` in Android

getenv

Added in API level 1

public static String getenv (String name)

Gets the value of the specified environment variable. An environment variable is a system-dependent external named value.

If a security manager exists, its checkPermission method is called with a RuntimePermission("getenv."+name) permission. This may result in a SecurityException being thrown. If no exception is thrown the value of the variable name is returned.

System properties and environment variables are both conceptually mappings between names and values. Both mechanisms can be used to pass user-defined information to a Java process. Environment variables have a more global effect, because they are visible to all descendants of the process which defines them, not just the immediate Java subprocess. They can have subtly different semantics, such as case insensitivity, on different operating systems. For these reasons, environment variables are more likely to have unintended side effects. It is best to use system properties where possible. Environment variables should be used when a global effect is desired, or when an external system interface requires an environment variable (such as PATH).

On UNIX systems the alphabetic case of name is typically significant, while on Microsoft Windows systems it is typically not. For example, the expression System.getenv("FOO").equals(System.getenv("foo")) is likely to be true on Microsoft Windows.

Parameters
`name`	`String`: the name of the environment variable

Returns
`String`	the string value of the variable, or `null` if the variable is not defined in the system environment

Throws
`NullPointerException`	if `name` is `null`
`SecurityException`	if a security manager exists and its `checkPermission` method doesn't allow access to the environment variable `name`

See also:

getenv

Added in API level 1

public static Map<String, String> getenv ()

Returns an unmodifiable string map view of the current system environment. The environment is a system-dependent mapping from names to values which is passed from parent to child processes.

If the system does not support environment variables, an empty map is returned.

The returned map will never contain null keys or values. Attempting to query the presence of a null key or value will throw a NullPointerException. Attempting to query the presence of a key or value which is not of type String will throw a ClassCastException.

The returned map and its collection views may not obey the general contract of the Object.equals and Object.hashCode methods.

The returned map is typically case-sensitive on all platforms.

If a security manager exists, its checkPermission method is called with a RuntimePermission("getenv.*") permission. This may result in a SecurityException being thrown.

When passing information to a Java subprocess, system properties are generally preferred over environment variables.

Returns
`Map<String, String>`	the environment as a map of variable names to values

Throws
`SecurityException`	if a security manager exists and its `checkPermission` method doesn't allow access to the process environment

See also:

identityHashCode

Added in API level 1

public static int identityHashCode (Object x)

Returns the same hash code for the given object as would be returned by the default method hashCode(), whether or not the given object's class overrides hashCode(). The hash code for the null reference is zero.

Parameters
`x`	`Object`: object for which the hashCode is to be calculated

Returns
`int`	the hashCode

inheritedChannel

Added in API level 1

public static Channel inheritedChannel ()

Returns the channel inherited from the entity that created this Java virtual machine.

This method returns the channel obtained by invoking the inheritedChannel method of the system-wide default SelectorProvider object.

In addition to the network-oriented channels described in inheritedChannel, this method may return other kinds of channels in the future.

Returns
`Channel`	The inherited channel, if any, otherwise `null`.

Throws
`IOException`	If an I/O error occurs
`SecurityException`	If a security manager is present and it does not permit access to the channel.

lineSeparator

Added in API level 19

public static String lineSeparator ()

Returns the system-dependent line separator string. It always returns the same value - the initial value of the system property line.separator.

On UNIX systems, it returns "\n"; on Microsoft Windows systems it returns "\r\n".

Returns
`String`	the system-dependent line separator string

load

Added in API level 1

public static void load (String filename)

Loads the native library specified by the filename argument. The filename argument must be an absolute path name. 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.

The call System.load(name) is effectively equivalent to the call:

 Runtime.getRuntime().load(name)

Parameters
`filename`	`String`: the file to load.

Throws
`SecurityException`	if a security manager exists and its `checkLink` method doesn't allow loading of the specified dynamic library
`UnsatisfiedLinkError`	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`	if `filename` is `null`

See also:

loadLibrary

Added in API level 1

public static void loadLibrary (String libname)

Loads the native library specified by the libname argument. The libname argument must not contain any platform specific prefix, file extension or path. If a native library called libname 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.

The call System.loadLibrary(name) is effectively equivalent to the call

 Runtime.getRuntime().loadLibrary(name)

Parameters
`libname`	`String`: the name of the library.

Throws
`SecurityException`	if a security manager exists and its `checkLink` method doesn't allow loading of the specified dynamic library
`UnsatisfiedLinkError`	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`	if `libname` is `null`

See also:

mapLibraryName

Added in API level 1

public static String mapLibraryName (String libname)

Maps a library name into a platform-specific string representing a native library.

Parameters
`libname`	`String`: the name of the library.

Returns
`String`	a platform-dependent native library name.

Throws
`NullPointerException`	if `libname` is `null`

See also:

nanoTime

Added in API level 1

public static long nanoTime ()

Returns the current value of the running Java Virtual Machine's high-resolution time source, in nanoseconds.

This method can only be used to measure elapsed time and is not related to any other notion of system or wall-clock time. The value returned represents nanoseconds since some fixed but arbitrary origin time (perhaps in the future, so values may be negative). The same origin is used by all invocations of this method in an instance of a Java virtual machine; other virtual machine instances are likely to use a different origin.

This method provides nanosecond precision, but not necessarily nanosecond resolution (that is, how frequently the value changes) - no guarantees are made except that the resolution is at least as good as that of currentTimeMillis().

Differences in successive calls that span greater than approximately 292 years (2⁶³ nanoseconds) will not correctly compute elapsed time due to numerical overflow.

The values returned by this method become meaningful only when the difference between two such values, obtained within the same instance of a Java virtual machine, is computed.

For example, to measure how long some code takes to execute:

 long startTime = System.nanoTime();
 // ... the code being measured ...
 long estimatedTime = System.nanoTime() - startTime;

To compare two nanoTime values

 long t0 = System.nanoTime();
 ...
 long t1 = System.nanoTime();

one should use t1 - t0 < 0, not t1 < t0, because of the possibility of numerical overflow.

The value returned by this method does not account for elapsed time during deep sleep. For timekeeping facilities available on Android see SystemClock.

Returns
`long`	the current value of the running Java Virtual Machine's high-resolution time source, in nanoseconds

runFinalization

Added in API level 1

public static 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 call System.runFinalization() is effectively equivalent to the call:

 Runtime.getRuntime().runFinalization()

See also:

Runtime.runFinalization()

runFinalizersOnExit

Added in API level 1
Deprecated in API level 15

public static void runFinalizersOnExit (boolean value)

This method was deprecated in API level 15.
This method is inherently unsafe. It may result in finalizers being called on live objects while other threads are concurrently manipulating those objects, resulting in erratic behavior or deadlock.

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.

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.

Parameters
`value`	`boolean`: indicating enabling or disabling of finalization

Throws
`SecurityException`	if a security manager exists and its `checkExit` method doesn't allow the exit.

See also:

setErr

Added in API level 1

public static void setErr (PrintStream err)

Reassigns the "standard" error output stream.

First, if there is a security manager, its checkPermission method is called with a RuntimePermission("setIO") permission to see if it's ok to reassign the "standard" error output stream.

Parameters
`err`	`PrintStream`: the new standard error output stream.

Throws
`SecurityException`	if a security manager exists and its `checkPermission` method doesn't allow reassigning of the standard error output stream.

See also:

setIn

Added in API level 1

public static void setIn (InputStream in)

Reassigns the "standard" input stream.

First, if there is a security manager, its checkPermission method is called with a RuntimePermission("setIO") permission to see if it's ok to reassign the "standard" input stream.

Parameters
`in`	`InputStream`: the new standard input stream.

Throws
`SecurityException`	if a security manager exists and its `checkPermission` method doesn't allow reassigning of the standard input stream.

See also:

setOut

Added in API level 1

public static void setOut (PrintStream out)

Reassigns the "standard" output stream.

First, if there is a security manager, its checkPermission method is called with a RuntimePermission("setIO") permission to see if it's ok to reassign the "standard" output stream.

Parameters
`out`	`PrintStream`: the new standard output stream

Throws
`SecurityException`	if a security manager exists and its `checkPermission` method doesn't allow reassigning of the standard output stream.

See also:

setProperties

Added in API level 1

public static void setProperties (Properties props)

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(String) for a list of such properties.

Parameters
`props`	`Properties`

setProperty

Added in API level 1

public static String setProperty (String key, 
                String value)

Sets the system property indicated by the specified key.

Parameters
`key`	`String`: the name of the system property.
`value`	`String`: the value of the system property.

Returns
`String`	the previous value of the system property, or `null` if it did not have one.

Throws
`SecurityException`	if a security manager exists and its `checkPermission` method doesn't allow setting of the specified property.
`NullPointerException`	if `key` or `value` is `null`.
`IllegalArgumentException`	if `key` is empty.

See also:

setSecurityManager

Added in API level 1

public static void setSecurityManager (SecurityManager s)

Throws SecurityException (except in case sm == null).

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 when passed a non-null SecurityManager

Parameters
`s`	`SecurityManager`: a security manager

Throws
`SecurityException`	always, unless `sm == null`