java.lang
Class System

java.lang.Object sample code for java.lang.Object definition code for java.lang.Object 
  extended by java.lang.System

public final class System
extends Object sample code for java.lang.Object definition code for java.lang.Object

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.

Since:
JDK1.0

Field Summary
static PrintStream sample code for java.io.PrintStream definition code for java.io.PrintStream err sample code for java.lang.System.err definition code for java.lang.System.err
          The "standard" error output stream.
static InputStream sample code for java.io.InputStream definition code for java.io.InputStream in sample code for java.lang.System.in definition code for java.lang.System.in
          The "standard" input stream.
static PrintStream sample code for java.io.PrintStream definition code for java.io.PrintStream out sample code for java.lang.System.out definition code for java.lang.System.out
          The "standard" output stream.
 
Method Summary
static void arraycopy sample code for java.lang.System.arraycopy(java.lang.Object, int, java.lang.Object, int, int) definition code for java.lang.System.arraycopy(java.lang.Object, int, java.lang.Object, int, int) (Object sample code for java.lang.Object definition code for java.lang.Object  src, int srcPos, Object sample code for java.lang.Object definition code for java.lang.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 sample code for java.lang.String definition code for java.lang.String clearProperty sample code for java.lang.System.clearProperty(java.lang.String) definition code for java.lang.System.clearProperty(java.lang.String) (String sample code for java.lang.String definition code for java.lang.String  key)
          Removes the system property indicated by the specified key.
static long currentTimeMillis sample code for java.lang.System.currentTimeMillis() definition code for java.lang.System.currentTimeMillis() ()
          Returns the current time in milliseconds.
static void exit sample code for java.lang.System.exit(int) definition code for java.lang.System.exit(int) (int status)
          Terminates the currently running Java Virtual Machine.
static void gc sample code for java.lang.System.gc() definition code for java.lang.System.gc() ()
          Runs the garbage collector.
static Map sample code for java.util.Map definition code for java.util.Map <String sample code for java.lang.String definition code for java.lang.String ,String sample code for java.lang.String definition code for java.lang.String > getenv sample code for java.lang.System.getenv() definition code for java.lang.System.getenv() ()
          Returns an unmodifiable string map view of the current system environment.
static String sample code for java.lang.String definition code for java.lang.String getenv sample code for java.lang.System.getenv(java.lang.String) definition code for java.lang.System.getenv(java.lang.String) (String sample code for java.lang.String definition code for java.lang.String  name)
          Gets the value of the specified environment variable.
static Properties sample code for java.util.Properties definition code for java.util.Properties getProperties sample code for java.lang.System.getProperties() definition code for java.lang.System.getProperties() ()
          Determines the current system properties.
static String sample code for java.lang.String definition code for java.lang.String getProperty sample code for java.lang.System.getProperty(java.lang.String) definition code for java.lang.System.getProperty(java.lang.String) (String sample code for java.lang.String definition code for java.lang.String  key)
          Gets the system property indicated by the specified key.
static String sample code for java.lang.String definition code for java.lang.String getProperty sample code for java.lang.System.getProperty(java.lang.String, java.lang.String) definition code for java.lang.System.getProperty(java.lang.String, java.lang.String) (String sample code for java.lang.String definition code for java.lang.String  key, String sample code for java.lang.String definition code for java.lang.String  def)
          Gets the system property indicated by the specified key.
static SecurityManager sample code for java.lang.SecurityManager definition code for java.lang.SecurityManager getSecurityManager sample code for java.lang.System.getSecurityManager() definition code for java.lang.System.getSecurityManager() ()
          Gets the system security interface.
static int identityHashCode sample code for java.lang.System.identityHashCode(java.lang.Object) definition code for java.lang.System.identityHashCode(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.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 sample code for java.nio.channels.Channel definition code for java.nio.channels.Channel inheritedChannel sample code for java.lang.System.inheritedChannel() definition code for java.lang.System.inheritedChannel() ()
          Returns the channel inherited from the entity that created this Java virtual machine.
static void load sample code for java.lang.System.load(java.lang.String) definition code for java.lang.System.load(java.lang.String) (String sample code for java.lang.String definition code for java.lang.String  filename)
          Loads a code file with the specified filename from the local file system as a dynamic library.
static void loadLibrary sample code for java.lang.System.loadLibrary(java.lang.String) definition code for java.lang.System.loadLibrary(java.lang.String) (String sample code for java.lang.String definition code for java.lang.String  libname)
          Loads the system library specified by the libname argument.
static String sample code for java.lang.String definition code for java.lang.String mapLibraryName sample code for java.lang.System.mapLibraryName(java.lang.String) definition code for java.lang.System.mapLibraryName(java.lang.String) (String sample code for java.lang.String definition code for java.lang.String  libname)
          Maps a library name into a platform-specific string representing a native library.
static long nanoTime sample code for java.lang.System.nanoTime() definition code for java.lang.System.nanoTime() ()
          Returns the current value of the most precise available system timer, in nanoseconds.
static void runFinalization sample code for java.lang.System.runFinalization() definition code for java.lang.System.runFinalization() ()
          Runs the finalization methods of any objects pending finalization.
static void runFinalizersOnExit sample code for java.lang.System.runFinalizersOnExit(boolean) definition code for java.lang.System.runFinalizersOnExit(boolean) (boolean value)
          Deprecated. 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 sample code for java.lang.System.setErr(java.io.PrintStream) definition code for java.lang.System.setErr(java.io.PrintStream) (PrintStream sample code for java.io.PrintStream definition code for java.io.PrintStream  err)
          Reassigns the "standard" error output stream.
static void setIn sample code for java.lang.System.setIn(java.io.InputStream) definition code for java.lang.System.setIn(java.io.InputStream) (InputStream sample code for java.io.InputStream definition code for java.io.InputStream  in)
          Reassigns the "standard" input stream.
static void setOut sample code for java.lang.System.setOut(java.io.PrintStream) definition code for java.lang.System.setOut(java.io.PrintStream) (PrintStream sample code for java.io.PrintStream definition code for java.io.PrintStream  out)
          Reassigns the "standard" output stream.
static void setProperties sample code for java.lang.System.setProperties(java.util.Properties) definition code for java.lang.System.setProperties(java.util.Properties) (Properties sample code for java.util.Properties definition code for java.util.Properties  props)
          Sets the system properties to the Properties argument.
static String sample code for java.lang.String definition code for java.lang.String setProperty sample code for java.lang.System.setProperty(java.lang.String, java.lang.String) definition code for java.lang.System.setProperty(java.lang.String, java.lang.String) (String sample code for java.lang.String definition code for java.lang.String  key, String sample code for java.lang.String definition code for java.lang.String  value)
          Sets the system property indicated by the specified key.
static void setSecurityManager sample code for java.lang.System.setSecurityManager(java.lang.SecurityManager) definition code for java.lang.System.setSecurityManager(java.lang.SecurityManager) (SecurityManager sample code for java.lang.SecurityManager definition code for java.lang.SecurityManager  s)
          Sets the System security.
 
Methods inherited from class java.lang.Object sample code for java.lang.Object definition code for java.lang.Object
clone sample code for java.lang.Object.clone() definition code for java.lang.Object.clone() , equals sample code for java.lang.Object.equals(java.lang.Object) definition code for java.lang.Object.equals(java.lang.Object) , finalize sample code for java.lang.Object.finalize() definition code for java.lang.Object.finalize() , getClass sample code for java.lang.Object.getClass() definition code for java.lang.Object.getClass() , hashCode sample code for java.lang.Object.hashCode() definition code for java.lang.Object.hashCode() , notify sample code for java.lang.Object.notify() definition code for java.lang.Object.notify() , notifyAll sample code for java.lang.Object.notifyAll() definition code for java.lang.Object.notifyAll() , toString sample code for java.lang.Object.toString() definition code for java.lang.Object.toString() , wait sample code for java.lang.Object.wait() definition code for java.lang.Object.wait() , wait sample code for java.lang.Object.wait(long) definition code for java.lang.Object.wait(long) , wait sample code for java.lang.Object.wait(long, int) definition code for java.lang.Object.wait(long, int)
 

Field Detail

in sample code for java.lang.System.in

public static final InputStream sample code for java.io.InputStream definition code for java.io.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 sample code for java.lang.System.out

public static final PrintStream sample code for java.io.PrintStream definition code for java.io.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:
PrintStream.println() sample code for java.io.PrintStream.println() definition code for java.io.PrintStream.println() , PrintStream.println(boolean) sample code for java.io.PrintStream.println(boolean) definition code for java.io.PrintStream.println(boolean) , PrintStream.println(char) sample code for java.io.PrintStream.println(char) definition code for java.io.PrintStream.println(char) , PrintStream.println(char[]) sample code for java.io.PrintStream.println(char[]) definition code for java.io.PrintStream.println(char[]) , PrintStream.println(double) sample code for java.io.PrintStream.println(double) definition code for java.io.PrintStream.println(double) , PrintStream.println(float) sample code for java.io.PrintStream.println(float) definition code for java.io.PrintStream.println(float) , PrintStream.println(int) sample code for java.io.PrintStream.println(int) definition code for java.io.PrintStream.println(int) , PrintStream.println(long) sample code for java.io.PrintStream.println(long) definition code for java.io.PrintStream.println(long) , PrintStream.println(java.lang.Object) sample code for java.io.PrintStream.println(java.lang.Object) definition code for java.io.PrintStream.println(java.lang.Object) , PrintStream.println(java.lang.String) sample code for java.io.PrintStream.println(java.lang.String) definition code for java.io.PrintStream.println(java.lang.String)

err sample code for java.lang.System.err

public static final PrintStream sample code for java.io.PrintStream definition code for java.io.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.

Method Detail

setIn sample code for java.lang.System.setIn(java.io.InputStream) definition code for java.lang.System.setIn(java.io.InputStream)

public static void setIn(InputStream sample code for java.io.InputStream definition code for java.io.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 - the new standard input stream.
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and its checkPermission method doesn't allow reassigning of the standard input stream.
Since:
JDK1.1
See Also:
SecurityManager.checkPermission(java.security.Permission) sample code for java.lang.SecurityManager.checkPermission(java.security.Permission) definition code for java.lang.SecurityManager.checkPermission(java.security.Permission) , RuntimePermission sample code for java.lang.RuntimePermission definition code for java.lang.RuntimePermission

setOut sample code for java.lang.System.setOut(java.io.PrintStream) definition code for java.lang.System.setOut(java.io.PrintStream)

public static void setOut(PrintStream sample code for java.io.PrintStream definition code for java.io.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 - the new standard output stream
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and its checkPermission method doesn't allow reassigning of the standard output stream.
Since:
JDK1.1
See Also:
SecurityManager.checkPermission(java.security.Permission) sample code for java.lang.SecurityManager.checkPermission(java.security.Permission) definition code for java.lang.SecurityManager.checkPermission(java.security.Permission) , RuntimePermission sample code for java.lang.RuntimePermission definition code for java.lang.RuntimePermission

setErr sample code for java.lang.System.setErr(java.io.PrintStream) definition code for java.lang.System.setErr(java.io.PrintStream)

public static void setErr(PrintStream sample code for java.io.PrintStream definition code for java.io.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 - the new standard error output stream.
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and its checkPermission method doesn't allow reassigning of the standard error output stream.
Since:
JDK1.1
See Also:
SecurityManager.checkPermission(java.security.Permission) sample code for java.lang.SecurityManager.checkPermission(java.security.Permission) definition code for java.lang.SecurityManager.checkPermission(java.security.Permission) , RuntimePermission sample code for java.lang.RuntimePermission definition code for java.lang.RuntimePermission

inheritedChannel sample code for java.lang.System.inheritedChannel() definition code for java.lang.System.inheritedChannel()

public static Channel sample code for java.nio.channels.Channel definition code for java.nio.channels.Channel  inheritedChannel()
                                throws IOException sample code for java.io.IOException definition code for java.io.IOException 
Returns the channel inherited from the entity that created this Java virtual machine.

This method returns the channel obtained by invoking the inheritedChannel sample code for java.nio.channels.spi.SelectorProvider.inheritedChannel() definition code for java.nio.channels.spi.SelectorProvider.inheritedChannel() method of the system-wide default SelectorProvider sample code for java.nio.channels.spi.SelectorProvider definition code for java.nio.channels.spi.SelectorProvider object.

In addition to the network-oriented channels described in inheritedChannel sample code for java.nio.channels.spi.SelectorProvider.inheritedChannel() definition code for java.nio.channels.spi.SelectorProvider.inheritedChannel() , this method may return other kinds of channels in the future.

Returns:
The inherited channel, if any, otherwise null.
Throws:
IOException sample code for java.io.IOException definition code for java.io.IOException - If an I/O error occurs
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - If a security manager is present and it does not permit access to the channel.
Since:
1.5

setSecurityManager sample code for java.lang.System.setSecurityManager(java.lang.SecurityManager) definition code for java.lang.System.setSecurityManager(java.lang.SecurityManager)

public static void setSecurityManager(SecurityManager sample code for java.lang.SecurityManager definition code for java.lang.SecurityManager  s)
Sets the System security.

If there is a security manager already installed, this method first calls the security manager's checkPermission method with a RuntimePermission("setSecurityManager") permission to ensure it's ok to replace the existing security manager. This may result in throwing a SecurityException.

Otherwise, the argument is established as the current security manager. If the argument is null and no security manager has been established, then no action is taken and the method simply returns.

Parameters:
s - the security manager.
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if the security manager has already been set and its checkPermission method doesn't allow it to be replaced.
See Also:
getSecurityManager() sample code for java.lang.System.getSecurityManager() definition code for java.lang.System.getSecurityManager() , SecurityManager.checkPermission(java.security.Permission) sample code for java.lang.SecurityManager.checkPermission(java.security.Permission) definition code for java.lang.SecurityManager.checkPermission(java.security.Permission) , RuntimePermission sample code for java.lang.RuntimePermission definition code for java.lang.RuntimePermission

getSecurityManager sample code for java.lang.System.getSecurityManager() definition code for java.lang.System.getSecurityManager()

public static SecurityManager sample code for java.lang.SecurityManager definition code for java.lang.SecurityManager  getSecurityManager()
Gets the system security interface.

Returns:
if a security manager has already been established for the current application, then that security manager is returned; otherwise, null is returned.
See Also:
setSecurityManager(java.lang.SecurityManager) sample code for java.lang.System.setSecurityManager(java.lang.SecurityManager) definition code for java.lang.System.setSecurityManager(java.lang.SecurityManager)

currentTimeMillis sample code for java.lang.System.currentTimeMillis() definition code for java.lang.System.currentTimeMillis()

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:
the difference, measured in milliseconds, between the current time and midnight, January 1, 1970 UTC.
See Also:
Date sample code for java.util.Date definition code for java.util.Date

nanoTime sample code for java.lang.System.nanoTime() definition code for java.lang.System.nanoTime()

public static long nanoTime()
Returns the current value of the most precise available system timer, 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 time (perhaps in the future, so values may be negative). This method provides nanosecond precision, but not necessarily nanosecond accuracy. No guarantees are made about how frequently values change. Differences in successive calls that span greater than approximately 292 years (263 nanoseconds) will not accurately compute elapsed time due to numerical overflow.

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

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

Returns:
The current value of the system timer, in nanoseconds.
Since:
1.5

arraycopy sample code for java.lang.System.arraycopy(java.lang.Object, int, java.lang.Object, int, int) definition code for java.lang.System.arraycopy(java.lang.Object, int, java.lang.Object, int, int)

public static void arraycopy(Object sample code for java.lang.Object definition code for java.lang.Object  src,
                             int srcPos,
                             Object sample code for java.lang.Object definition code for java.lang.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:

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

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 - the source array.
srcPos - starting position in the source array.
dest - the destination array.
destPos - starting position in the destination data.
length - the number of array elements to be copied.
Throws:
IndexOutOfBoundsException sample code for java.lang.IndexOutOfBoundsException definition code for java.lang.IndexOutOfBoundsException - if copying would cause access of data outside array bounds.
ArrayStoreException sample code for java.lang.ArrayStoreException definition code for java.lang.ArrayStoreException - if an element in the src array could not be stored into the dest array because of a type mismatch.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if either src or dest is null.

identityHashCode sample code for java.lang.System.identityHashCode(java.lang.Object) definition code for java.lang.System.identityHashCode(java.lang.Object)

public static int identityHashCode(Object sample code for java.lang.Object definition code for java.lang.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 for which the hashCode is to be calculated
Returns:
the hashCode
Since:
JDK1.1

getProperties sample code for java.lang.System.getProperties() definition code for java.lang.System.getProperties()

public static Properties sample code for java.util.Properties definition code for java.util.Properties  getProperties()
Determines the current system properties.

First, if there is a security manager, its checkPropertiesAccess method is called with no arguments. This may result in a security exception.

The current set of system properties for use by the getProperty(String) sample code for java.lang.System.getProperty(java.lang.String) definition code for java.lang.System.getProperty(java.lang.String) method is returned as a Properties object. If there is no current set of system properties, a set of system properties is first created and initialized. This set of system properties always includes values for the following keys:

Key Description of Associated Value
java.version Java Runtime Environment version
java.vendor Java Runtime Environment vendor
java.vendor.url Java vendor URL
java.home Java installation directory
java.vm.specification.version Java Virtual Machine specification version
java.vm.specification.vendor Java Virtual Machine specification vendor
java.vm.specification.name Java Virtual Machine specification name
java.vm.version Java Virtual Machine implementation version
java.vm.vendor Java Virtual Machine implementation vendor
java.vm.name Java Virtual Machine implementation name
java.specification.version Java Runtime Environment specification version
java.specification.vendor Java Runtime Environment specification vendor
java.specification.name Java Runtime Environment specification name
java.class.version Java class format version number
java.class.path Java class path
java.library.path List of paths to search when loading libraries
java.io.tmpdir Default temp file path
java.compiler Name of JIT compiler to use
java.ext.dirs Path of extension directory or directories
os.name Operating system name
os.arch Operating system architecture
os.version Operating system version
file.separator File separator ("/" on UNIX)
path.separator Path separator (":" on UNIX)
line.separator Line separator ("\n" on UNIX)
user.name User's account name
user.home User's home directory
user.dir User's current working directory

Multiple paths in a system property value are separated by the path separator character of the platform.

Note that even if the security manager does not permit the getProperties operation, it may choose to permit the getProperty(String) sample code for java.lang.System.getProperty(java.lang.String) definition code for java.lang.System.getProperty(java.lang.String) operation.

Returns:
the system properties
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and its checkPropertiesAccess method doesn't allow access to the system properties.
See Also:
setProperties(java.util.Properties) sample code for java.lang.System.setProperties(java.util.Properties) definition code for java.lang.System.setProperties(java.util.Properties) , SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException , SecurityManager.checkPropertiesAccess() sample code for java.lang.SecurityManager.checkPropertiesAccess() definition code for java.lang.SecurityManager.checkPropertiesAccess() , Properties sample code for java.util.Properties definition code for java.util.Properties

setProperties sample code for java.lang.System.setProperties(java.util.Properties) definition code for java.lang.System.setProperties(java.util.Properties)

public static void setProperties(Properties sample code for java.util.Properties definition code for java.util.Properties  props)
Sets the system properties to the Properties argument.

First, if there is a security manager, its checkPropertiesAccess method is called with no arguments. This may result in a security exception.

The argument becomes the current set of system properties for use by the getProperty(String) sample code for java.lang.System.getProperty(java.lang.String) definition code for java.lang.System.getProperty(java.lang.String) method. If the argument is null, then the current set of system properties is forgotten.

Parameters:
props - the new system properties.
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and its checkPropertiesAccess method doesn't allow access to the system properties.
See Also:
getProperties() sample code for java.lang.System.getProperties() definition code for java.lang.System.getProperties() , Properties sample code for java.util.Properties definition code for java.util.Properties , SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException , SecurityManager.checkPropertiesAccess() sample code for java.lang.SecurityManager.checkPropertiesAccess() definition code for java.lang.SecurityManager.checkPropertiesAccess()

getProperty sample code for java.lang.System.getProperty(java.lang.String) definition code for java.lang.System.getProperty(java.lang.String)

public static String sample code for java.lang.String definition code for java.lang.String  getProperty(String sample code for java.lang.String definition code for java.lang.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 - the name of the system property.
Returns:
the string value of the system property, or null if there is no property with that key.
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and its checkPropertyAccess method doesn't allow access to the specified system property.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if key is null.
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - if key is empty.
See Also:
setProperty(java.lang.String, java.lang.String) sample code for java.lang.System.setProperty(java.lang.String, java.lang.String) definition code for java.lang.System.setProperty(java.lang.String, java.lang.String) , SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException , SecurityManager.checkPropertyAccess(java.lang.String) sample code for java.lang.SecurityManager.checkPropertyAccess(java.lang.String) definition code for java.lang.SecurityManager.checkPropertyAccess(java.lang.String) , getProperties() sample code for java.lang.System.getProperties() definition code for java.lang.System.getProperties()

getProperty sample code for java.lang.System.getProperty(java.lang.String, java.lang.String) definition code for java.lang.System.getProperty(java.lang.String, java.lang.String)

public static String sample code for java.lang.String definition code for java.lang.String  getProperty(String sample code for java.lang.String definition code for java.lang.String  key,
                                 String sample code for java.lang.String definition code for java.lang.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 - the name of the system property.
def - a default value.
Returns:
the string value of the system property, or the default value if there is no property with that key.
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and its checkPropertyAccess method doesn't allow access to the specified system property.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if key is null.
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - if key is empty.
See Also:
setProperty(java.lang.String, java.lang.String) sample code for java.lang.System.setProperty(java.lang.String, java.lang.String) definition code for java.lang.System.setProperty(java.lang.String, java.lang.String) , SecurityManager.checkPropertyAccess(java.lang.String) sample code for java.lang.SecurityManager.checkPropertyAccess(java.lang.String) definition code for java.lang.SecurityManager.checkPropertyAccess(java.lang.String) , getProperties() sample code for java.lang.System.getProperties() definition code for java.lang.System.getProperties()

setProperty sample code for java.lang.System.setProperty(java.lang.String, java.lang.String) definition code for java.lang.System.setProperty(java.lang.String, java.lang.String)

public static String sample code for java.lang.String definition code for java.lang.String  setProperty(String sample code for java.lang.String definition code for java.lang.String  key,
                                 String sample code for java.lang.String definition code for java.lang.String  value)
Sets 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 set to the given value.

Parameters:
key - the name of the system property.
value - the value of the system property.
Returns:
the previous value of the system property, or null if it did not have one.
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and its checkPermission method doesn't allow setting of the specified property.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if key or value is null.
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - if key is empty.
Since:
1.2
See Also:
getProperty(java.lang.String) sample code for java.lang.System.getProperty(java.lang.String) definition code for java.lang.System.getProperty(java.lang.String) , getProperty(java.lang.String) sample code for java.lang.System.getProperty(java.lang.String) definition code for java.lang.System.getProperty(java.lang.String) , getProperty(java.lang.String, java.lang.String) sample code for java.lang.System.getProperty(java.lang.String, java.lang.String) definition code for java.lang.System.getProperty(java.lang.String, java.lang.String) , PropertyPermission sample code for java.util.PropertyPermission definition code for java.util.PropertyPermission , SecurityManager.checkPermission(java.security.Permission) sample code for java.lang.SecurityManager.checkPermission(java.security.Permission) definition code for java.lang.SecurityManager.checkPermission(java.security.Permission)

clearProperty sample code for java.lang.System.clearProperty(java.lang.String) definition code for java.lang.System.clearProperty(java.lang.String)

public static String sample code for java.lang.String definition code for java.lang.String  clearProperty(String sample code for java.lang.String definition code for java.lang.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 - the name of the system property to be removed.
Returns:
the previous string value of the system property, or null if there was no property with that key.
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and its checkPropertyAccess method doesn't allow access to the specified system property.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if key is null.
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - if key is empty.
Since:
1.5
See Also:
getProperty(java.lang.String) sample code for java.lang.System.getProperty(java.lang.String) definition code for java.lang.System.getProperty(java.lang.String) , setProperty(java.lang.String, java.lang.String) sample code for java.lang.System.setProperty(java.lang.String, java.lang.String) definition code for java.lang.System.setProperty(java.lang.String, java.lang.String) , Properties sample code for java.util.Properties definition code for java.util.Properties , SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException , SecurityManager.checkPropertiesAccess() sample code for java.lang.SecurityManager.checkPropertiesAccess() definition code for java.lang.SecurityManager.checkPropertiesAccess()

getenv sample code for java.lang.System.getenv(java.lang.String) definition code for java.lang.System.getenv(java.lang.String)

public static String sample code for java.lang.String definition code for java.lang.String  getenv(String sample code for java.lang.String definition code for java.lang.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 sample code for java.lang.SecurityManager.checkPermission(java.security.Permission) definition code for java.lang.SecurityManager.checkPermission(java.security.Permission) method is called with a RuntimePermission sample code for java.lang.RuntimePermission definition code for java.lang.RuntimePermission ("getenv."+name) permission. This may result in a SecurityException sample code for java.lang.SecurityException definition code for java.lang.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 - the name of the environment variable
Returns:
the string value of the variable, or null if the variable is not defined in the system environment
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if name is null
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and its checkPermission sample code for java.lang.SecurityManager.checkPermission(java.security.Permission) definition code for java.lang.SecurityManager.checkPermission(java.security.Permission) method doesn't allow access to the environment variable name
See Also:
getenv() sample code for java.lang.System.getenv() definition code for java.lang.System.getenv() , ProcessBuilder.environment() sample code for java.lang.ProcessBuilder.environment() definition code for java.lang.ProcessBuilder.environment()

getenv sample code for java.lang.System.getenv() definition code for java.lang.System.getenv()

public static Map sample code for java.util.Map definition code for java.util.Map <String sample code for java.lang.String definition code for java.lang.String ,String sample code for java.lang.String definition code for java.lang.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 sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException . Attempting to query the presence of a key or value which is not of type String sample code for java.lang.String definition code for java.lang.String will throw a ClassCastException sample code for java.lang.ClassCastException definition code for java.lang.ClassCastException .

The returned map and its collection views may not obey the general contract of the Object.equals(java.lang.Object) sample code for java.lang.Object.equals(java.lang.Object) definition code for java.lang.Object.equals(java.lang.Object) and Object.hashCode() sample code for java.lang.Object.hashCode() definition code for java.lang.Object.hashCode() methods.

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

If a security manager exists, its checkPermission sample code for java.lang.SecurityManager.checkPermission(java.security.Permission) definition code for java.lang.SecurityManager.checkPermission(java.security.Permission) method is called with a RuntimePermission sample code for java.lang.RuntimePermission definition code for java.lang.RuntimePermission ("getenv.*") permission. This may result in a SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException being thrown.

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

Returns:
the environment as a map of variable names to values
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and its checkPermission sample code for java.lang.SecurityManager.checkPermission(java.security.Permission) definition code for java.lang.SecurityManager.checkPermission(java.security.Permission) method doesn't allow access to the process environment
Since:
1.5
See Also:
getenv(String) sample code for java.lang.System.getenv(java.lang.String) definition code for java.lang.System.getenv(java.lang.String) , ProcessBuilder.environment() sample code for java.lang.ProcessBuilder.environment() definition code for java.lang.ProcessBuilder.environment()

exit sample code for java.lang.System.exit(int) definition code for java.lang.System.exit(int)

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 - exit status.
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and its checkExit method doesn't allow exit with the specified status.
See Also:
Runtime.exit(int) sample code for java.lang.Runtime.exit(int) definition code for java.lang.Runtime.exit(int)

gc sample code for java.lang.System.gc() definition code for java.lang.System.gc()

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()
 

See Also:
Runtime.gc() sample code for java.lang.Runtime.gc() definition code for java.lang.Runtime.gc()

runFinalization sample code for java.lang.System.runFinalization() definition code for java.lang.System.runFinalization()

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() sample code for java.lang.Runtime.runFinalization() definition code for java.lang.Runtime.runFinalization()

runFinalizersOnExit sample code for java.lang.System.runFinalizersOnExit(boolean) definition code for java.lang.System.runFinalizersOnExit(boolean)

@Deprecated
public static void runFinalizersOnExit(boolean value)
Deprecated. 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 - indicating enabling or disabling of finalization
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and its checkExit method doesn't allow the exit.
Since:
JDK1.1
See Also:
Runtime.exit(int) sample code for java.lang.Runtime.exit(int) definition code for java.lang.Runtime.exit(int) , Runtime.gc() sample code for java.lang.Runtime.gc() definition code for java.lang.Runtime.gc() , SecurityManager.checkExit(int) sample code for java.lang.SecurityManager.checkExit(int) definition code for java.lang.SecurityManager.checkExit(int)

load sample code for java.lang.System.load(java.lang.String) definition code for java.lang.System.load(java.lang.String)

public static void load(String sample code for java.lang.String definition code for java.lang.String  filename)
Loads a code file with the specified filename from the local file system as a dynamic library. The filename argument must be a complete path name.

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

 Runtime.getRuntime().load(name)
 

Parameters:
filename - the file to load.
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and its checkLink method doesn't allow loading of the specified dynamic library
UnsatisfiedLinkError sample code for java.lang.UnsatisfiedLinkError definition code for java.lang.UnsatisfiedLinkError - if the file does not exist.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if filename is null
See Also:
Runtime.load(java.lang.String) sample code for java.lang.Runtime.load(java.lang.String) definition code for java.lang.Runtime.load(java.lang.String) , SecurityManager.checkLink(java.lang.String) sample code for java.lang.SecurityManager.checkLink(java.lang.String) definition code for java.lang.SecurityManager.checkLink(java.lang.String)

loadLibrary sample code for java.lang.System.loadLibrary(java.lang.String) definition code for java.lang.System.loadLibrary(java.lang.String)

public static void loadLibrary(String sample code for java.lang.String definition code for java.lang.String  libname)
Loads the system library specified by the libname argument. The manner in which a library name is mapped to the actual system library is system dependent.

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

 Runtime.getRuntime().loadLibrary(name)
 

Parameters:
libname - the name of the library.
Throws:
SecurityException sample code for java.lang.SecurityException definition code for java.lang.SecurityException - if a security manager exists and its checkLink method doesn't allow loading of the specified dynamic library
UnsatisfiedLinkError sample code for java.lang.UnsatisfiedLinkError definition code for java.lang.UnsatisfiedLinkError - if the library does not exist.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if libname is null
See Also:
Runtime.loadLibrary(java.lang.String) sample code for java.lang.Runtime.loadLibrary(java.lang.String) definition code for java.lang.Runtime.loadLibrary(java.lang.String) , SecurityManager.checkLink(java.lang.String) sample code for java.lang.SecurityManager.checkLink(java.lang.String) definition code for java.lang.SecurityManager.checkLink(java.lang.String)

mapLibraryName sample code for java.lang.System.mapLibraryName(java.lang.String) definition code for java.lang.System.mapLibraryName(java.lang.String)

public static String sample code for java.lang.String definition code for java.lang.String  mapLibraryName(String sample code for java.lang.String definition code for java.lang.String  libname)
Maps a library name into a platform-specific string representing a native library.

Parameters:
libname - the name of the library.
Returns:
a platform-dependent native library name.
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if libname is null
Since:
1.2
See Also:
loadLibrary(java.lang.String) sample code for java.lang.System.loadLibrary(java.lang.String) definition code for java.lang.System.loadLibrary(java.lang.String) , ClassLoader.findLibrary(java.lang.String) sample code for java.lang.ClassLoader.findLibrary(java.lang.String) definition code for java.lang.ClassLoader.findLibrary(java.lang.String)