ThreadLocal并不是一个Thread，而是Thread的 ，也许把它命名为ThreadLocalVariable更容易让人理解一些。

所以，在Java中编写线程局部变量的代码相对来说要笨拙一些，因此造成线程局部变量没有在Java开发者中得到很好的普及。

ThreadLocal的接口方法

ThreadLocal类接口很简单，只有4个方法，我们先来了解一下：

void set(Object value)

public void remove()

将当前线程 的值删除，目的是为了减少内存的占用。

 

ThreadLocal的原理

在ThreadLocal类中有一个Map，用于

存储每一个线程的变量的副本。比如下面的示例实现：

public class ThreadLocal

private Map values = Collections.synchronizedMap(new HashMap());

public Object get()

{

Thread curThread = Thread.currentThread();

Object o = values.get(curThread);

if (o == null && !values.containsKey(curThread))

{

o = initialValue();

values.put(curThread, o);

}

values.put(Thread.currentThread(), newValue);

return o ;

}

public Object initialValue()

{

return null;

}

}

 

 

演示代码

 

public class ThreadLocalExample {    public static class MyRunnable implements Runnable {        private ThreadLocal
        
          threadLocal =        new ThreadLocal
         
          ();        int local = 0;        @Override        public void run() {            threadLocal.set((int) (Math.random() * 100D));            local = (int) (Math.random() * 100D);            try {                Thread.sleep(2000);            } catch (InterruptedException e) {            }            System.out.println("threadLocal:" +threadLocal.get());            System.out.println("local:" +local);        }    }    public static void main(String[] args) {        MyRunnable sharedRunnableInstance = new MyRunnable();        Thread thread1 = new Thread(sharedRunnableInstance);        Thread thread2 = new Thread(sharedRunnableInstance);        thread1.start();        thread2.start();        try {            thread1.join();            thread2.join();         } catch (InterruptedException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } // wait for thread 1 to terminate        // wait for thread 2 to terminate    }}