System

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java.lang
Class System

java.lang.Object
  java.lang.System

public final class System
extends Object

System represents system-wide resources; things that represent the general environment. As such, all methods are static.

Since:: 1.0

Field Summary

static java.io.PrintStream err
          The standard output PrintStream.

static java.io.InputStream in
          The standard InputStream.

static java.io.PrintStream out
          The standard output PrintStream.

Constructor Summary

private System()
          This class is uninstantiable.

Method Summary

static void arraycopy(Object src, int srcStart, Object dest, int destStart, int len)
          Copy one array onto another from src[srcStart] ...

static String clearProperty(String key)
          Remove a single system property by name.

static long currentTimeMillis()
          Get the current time, measured in the number of milliseconds from the beginning of Jan.

static void exit(int status)
          Terminate the Virtual Machine.

static void gc()
          Calls the garbage collector.

static String getenv(String name)
          Gets the value of an environment variable.

static java.util.Properties getProperties()
          Get all the system properties at once.

static String getProperty(String key)
          Get a single system property by name.

static String getProperty(String key, String def)
          Get a single system property by name.

static SecurityManager getSecurityManager()
          Get the current SecurityManager.

static int identityHashCode(Object o)
          Get a hash code computed by the VM for the Object.

static void load(String filename)
          Load a code file using its explicit system-dependent filename.

static void loadLibrary(String libname)
          Load a library using its explicit system-dependent filename.

static String mapLibraryName(String libname)
          Convert a library name to its platform-specific variant.

static void runFinalization()
          Runs object finalization on pending objects.

static void runFinalizersOnExit(boolean finalizeOnExit)
          Deprecated. never rely on finalizers to do a clean, thread-safe, mop-up from your code

static void setErr(java.io.PrintStream err)
          Set err 55 to a new PrintStream.

static void setIn(java.io.InputStream in)
          Set in 55 to a new InputStream.

static void setOut(java.io.PrintStream out)
          Set out 55 to a new PrintStream.

static void setProperties(java.util.Properties properties)
          Set all the system properties at once.

static String setProperty(String key, String value)
          Set a single system property by name.

static void setSecurityManager(SecurityManager sm)
          Set the current SecurityManager.

Methods inherited from class java.lang.Object

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

Field Detail

in

public static final java.io.InputStream in

The standard InputStream. This is assigned at startup and starts its life perfectly valid. Although it is marked final, you can change it using setIn(InputStream) 55 through some hefty VM magic.

This corresponds to the C stdin and C++ cin variables, which typically input from the keyboard, but may be used to pipe input from other processes or files. That should all be transparent to you, however.

out

public static final java.io.PrintStream out

The standard output PrintStream. This is assigned at startup and starts its life perfectly valid. Although it is marked final, you can change it using setOut(PrintStream) 55 through some hefty VM magic.

This corresponds to the C stdout and C++ cout variables, which typically output normal messages to the screen, but may be used to pipe output to other processes or files. That should all be transparent to you, however.

err

public static final java.io.PrintStream err

The standard output PrintStream. This is assigned at startup and starts its life perfectly valid. Although it is marked final, you can change it using setErr(PrintStream) 55 through some hefty VM magic.

This corresponds to the C stderr and C++ cerr variables, which typically output error messages to the screen, but may be used to pipe output to other processes or files. That should all be transparent to you, however.

Constructor Detail

System

private System()

This class is uninstantiable.

Method Detail

setIn

public static void setIn(java.io.InputStream in)

Set in 55 to a new InputStream. This uses some VM magic to change a "final" variable, so naturally there is a security check, RuntimePermission("setIO").

Since:: 1.1

setOut

public static void setOut(java.io.PrintStream out)

Set out 55 to a new PrintStream. This uses some VM magic to change a "final" variable, so naturally there is a security check, RuntimePermission("setIO").

Since:: 1.1

setErr

public static void setErr(java.io.PrintStream err)

Set err 55 to a new PrintStream. This uses some VM magic to change a "final" variable, so naturally there is a security check, RuntimePermission("setIO").

Since:: 1.1

setSecurityManager

public static void setSecurityManager(SecurityManager sm)

Set the current SecurityManager. If a security manager already exists, then RuntimePermission("setSecurityManager") is checked first. Since this permission is denied by the default security manager, setting the security manager is often an irreversible action. Spec Note: Don't ask me, I didn't write it. It looks pretty vulnerable; whoever gets to the gate first gets to set the policy. There is probably some way to set the original security manager as a command line argument to the VM, but I don't know it.

getSecurityManager

public static SecurityManager getSecurityManager()

Get the current SecurityManager. If the SecurityManager has not been set yet, then this method returns null.

currentTimeMillis

public static long currentTimeMillis()

Get the current time, measured in the number of milliseconds from the beginning of Jan. 1, 1970. This is gathered from the system clock, with any attendant incorrectness (it may be timezone dependent).

arraycopy

public static void arraycopy(Object src,
                             int srcStart,
                             Object dest,
                             int destStart,
                             int len)

Copy one array onto another from src[srcStart] ... src[srcStart+len-1] to dest[destStart] ... dest[destStart+len-1]. First, the arguments are validated: neither array may be null, they must be of compatible types, and the start and length must fit within both arrays. Then the copying starts, and proceeds through increasing slots. If src and dest are the same array, this will appear to copy the data to a temporary location first. An ArrayStoreException in the middle of copying will leave earlier elements copied, but later elements unchanged.

identityHashCode

public static int identityHashCode(Object o)

Get a hash code computed by the VM for the Object. This hash code will be the same as Object's hashCode() method. It is usually some convolution of the pointer to the Object internal to the VM. It follows standard hash code rules, in that it will remain the same for a given Object for the lifetime of that Object.

Since:: 1.1

getProperties

public static java.util.Properties getProperties()

Get all the system properties at once. A security check may be performed, checkPropertiesAccess. Note that a security manager may allow getting a single property, but not the entire group.

The required properties include:

java.version: Java version number
java.vendor: Java vendor specific string
java.vendor.url: Java vendor URL
java.home: Java installation directory
java.vm.specification.version: VM Spec version
java.vm.specification.vendor: VM Spec vendor
java.vm.specification.name: VM Spec name
java.vm.version: VM implementation version
java.vm.vendor: VM implementation vendor
java.vm.name: VM implementation name
java.specification.version: Java Runtime Environment version
java.specification.vendor: Java Runtime Environment vendor
java.specification.name: Java Runtime Environment name
java.class.version: Java class version number
java.class.path: Java classpath
java.library.path: Path for finding Java libraries
java.io.tmpdir: Default temp file path
java.compiler: Name of JIT to use
java.ext.dirs: Java extension path
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 account name
user.home: User home directory
user.dir: User's current working directory

In addition, gnu defines several other properties, where ? stands for each character in '0' through '9':

gnu.classpath.home: Path to the classpath libraries.
gnu.classpath.version: Version of the classpath libraries.
gnu.classpath.vm.shortname: Succinct version of the VM name; used for finding property files in file system
gnu.classpath.home.url: Base URL; used for finding property files in file system
gnu.cpu.endian: big or little
gnu.java.io.encoding_scheme_alias.iso-8859-?: 8859_?
gnu.java.io.encoding_scheme_alias.iso8859_?: 8859_?
gnu.java.io.encoding_scheme_alias.iso-latin-_?: 8859_?
gnu.java.io.encoding_scheme_alias.latin?: 8859_?
gnu.java.io.encoding_scheme_alias.utf-8: UTF8

setProperties

public static void setProperties(java.util.Properties properties)

Set all the system properties at once. A security check may be performed, checkPropertiesAccess. Note that a security manager may allow setting a single property, but not the entire group. An argument of null resets the properties to the startup default.

getProperty

public static String getProperty(String key)

Get a single system property by name. A security check may be performed, checkPropertyAccess(key).

getProperty

public static String getProperty(String key,
                                 String def)

Get a single system property by name. A security check may be performed, checkPropertyAccess(key).

setProperty

public static String setProperty(String key,
                                 String value)

Set a single system property by name. A security check may be performed, checkPropertyAccess(key, "write").

Since:: 1.2

clearProperty

public static String clearProperty(String key)

Remove a single system property by name. A security check may be performed, checkPropertyAccess(key, "write").

Since:: 1.5

getenv

public static String getenv(String name)

Gets the value of an environment variable.

Since:: 1.5

exit

public static void exit(int status)

Terminate the Virtual Machine. This just calls Runtime.getRuntime().exit(status), and never returns. Obviously, a security check is in order, checkExit.

gc

public static void gc()

Calls the garbage collector. This is only a hint, and it is up to the implementation what this hint suggests, but it usually causes a best-effort attempt to reclaim unused memory from discarded objects. This calls Runtime.getRuntime().gc().

runFinalization

public static void runFinalization()

Runs object finalization on pending objects. This is only a hint, and it is up to the implementation what this hint suggests, but it usually causes a best-effort attempt to run finalizers on all objects ready to be reclaimed. This calls Runtime.getRuntime().runFinalization().

runFinalizersOnExit

public static void runFinalizersOnExit(boolean finalizeOnExit)

Deprecated. never rely on finalizers to do a clean, thread-safe, mop-up from your code

Tell the Runtime whether to run finalization before exiting the JVM. This is inherently unsafe in multi-threaded applications, since it can force initialization on objects which are still in use by live threads, leading to deadlock; therefore this is disabled by default. There may be a security check, checkExit(0). This calls Runtime.runFinalizersOnExit().

Since:: 1.1

load

public static void load(String filename)

Load a code file using its explicit system-dependent filename. A security check may be performed, checkLink. This just calls Runtime.getRuntime().load(filename).

The library is loaded using the class loader associated with the class associated with the invoking method.

loadLibrary

public static void loadLibrary(String libname)

Load a library using its explicit system-dependent filename. A security check may be performed, checkLink. This just calls Runtime.getRuntime().load(filename).

The library is loaded using the class loader associated with the class associated with the invoking method.

mapLibraryName

public static String mapLibraryName(String libname)

Convert a library name to its platform-specific variant.

Since:: 1.2

Overview

Package

Class

Use

Deprecated

Index

Home >> All >> java >> [ lang overview ]

PREV CLASS NEXT CLASS

SUMMARY:

JAVADOC |

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DETAIL: FIELD | CONSTR | METHOD

Field Summary
`static java.io.PrintStream`	`err` The standard output PrintStream.
`static java.io.InputStream`	`in` The standard InputStream.
`static java.io.PrintStream`	`out` The standard output PrintStream.

Constructor Summary
`private`	`System()` This class is uninstantiable.

Method Summary
`static void`	`arraycopy(Object src, int srcStart, Object dest, int destStart, int len)` Copy one array onto another from `src[srcStart]` ...
`static String`	`clearProperty(String key)` Remove a single system property by name.
`static long`	`currentTimeMillis()` Get the current time, measured in the number of milliseconds from the beginning of Jan.
`static void`	`exit(int status)` Terminate the Virtual Machine.
`static void`	`gc()` Calls the garbage collector.
`static String`	`getenv(String name)` Gets the value of an environment variable.
`static java.util.Properties`	`getProperties()` Get all the system properties at once.
`static String`	`getProperty(String key)` Get a single system property by name.
`static String`	`getProperty(String key, String def)` Get a single system property by name.
`static SecurityManager`	`getSecurityManager()` Get the current SecurityManager.
`static int`	`identityHashCode(Object o)` Get a hash code computed by the VM for the Object.
`static void`	`load(String filename)` Load a code file using its explicit system-dependent filename.
`static void`	`loadLibrary(String libname)` Load a library using its explicit system-dependent filename.
`static String`	`mapLibraryName(String libname)` Convert a library name to its platform-specific variant.
`static void`	`runFinalization()` Runs object finalization on pending objects.
`static void`	`runFinalizersOnExit(boolean finalizeOnExit)` Deprecated. never rely on finalizers to do a clean, thread-safe, mop-up from your code
`static void`	`setErr(java.io.PrintStream err)` Set `err` 55 to a new PrintStream.
`static void`	`setIn(java.io.InputStream in)` Set `in` 55 to a new InputStream.
`static void`	`setOut(java.io.PrintStream out)` Set `out` 55 to a new PrintStream.
`static void`	`setProperties(java.util.Properties properties)` Set all the system properties at once.
`static String`	`setProperty(String key, String value)` Set a single system property by name.
`static void`	`setSecurityManager(SecurityManager sm)` Set the current SecurityManager.

java.lang Class System

in

out

err

System

setIn

setOut

setErr

setSecurityManager

getSecurityManager

currentTimeMillis

arraycopy

identityHashCode

getProperties

setProperties

getProperty

getProperty

setProperty

clearProperty

getenv

exit

gc

runFinalization

runFinalizersOnExit

load

loadLibrary

mapLibraryName

java.lang
Class System