ThreadLocal并不是一个Thread，而是Thread的局部变量，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()
将当前线程局部变量的值删除，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<Integer> threadLocal =
new ThreadLocal<Integer>();
int local = ;
@Override
public void run() {
threadLocal.set((int) (Math.random() * 100D));
local = (int) (Math.random() * 100D);
try {
Thread.sleep();
} 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
}
}