Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class ThreadLocal - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

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java.lang
Class ThreadLocal

java.lang.Object
  |
  +--java.lang.ThreadLocal

Direct Known Subclasses:: InheritableThreadLocal

public class ThreadLocal
extends Object

This class provides ThreadLocal variables. These variables differ from their normal counterparts in that each thread that accesses one (via its get or set method) has its own, independently initialized copy of the variable. ThreadLocal objects are typically private static variables in classes that wish to associate state with a thread (e.g., a user ID or Transaction ID).

Each thread holds an implicit reference to its copy of a ThreadLocal as long as the thread is alive and the ThreadLocal object is accessible; after a thread goes away, all of its copies of ThreadLocal variables are subject to garbage collection (unless other references to these copies exist).

Since:: JDK1.2

Constructor Summary

ThreadLocal()
          Creates a ThreadLocal variable.

Method Summary

Object get()
          Returns the value in the calling thread's copy of this ThreadLocal variable.

protected Object initialValue()
          Returns the calling thread's initial value for this ThreadLocal variable.

void set(Object value)
          Sets the calling thread's instance of this ThreadLocal variable to the given value.

Methods inherited from class java.lang.Object

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

Constructor Detail

ThreadLocal

public ThreadLocal()

Creates a ThreadLocal variable.

Method Detail

initialValue

protected Object initialValue()

Returns the calling thread's initial value for this ThreadLocal variable. This method will be called once per accessing thread for each ThreadLocal, the first time each thread accesses the variable with get or set. If the programmer desires ThreadLocal variables to be initialized to some value other than null, ThreadLocal must be subclassed, and this method overridden. Typically, an anonymous inner class will be used. Typical implementations of initialValue will call an appropriate constructor and return the newly constructed object.

get

public Object get()

Returns the value in the calling thread's copy of this ThreadLocal variable. Creates and initializes the copy if this is the first time the thread has called this method.

set

public void set(Object value)

Sets the calling thread's instance of this ThreadLocal variable to the given value. This is only used to change the value from the one assigned by the initialValue method, and many applications will have no need for this functionality.

Parameters:: value - the value to be stored in the calling threads' copy of this ThreadLocal.