ThreadLocal

运行代码

public class ThreadLocalTest {
    public static class MyRunnable implements Runnable {
        @Override
        public void run() {
            ThreadLocalTest.test();
        }
    }

    public static void main(String[] args) {
        MyRunnable sharedRunnableInstance = new MyRunnable();
        Thread thread1 = new Thread(sharedRunnableInstance);
        Thread thread2 = new Thread(sharedRunnableInstance);
        thread1.start();
        thread1.run();
        thread1.run();
        thread2.start();
        thread2.run();
    }

    private static ThreadLocal threadLocal = new ThreadLocal();

    private static void test() {
        if (threadLocal.get() == null) {
            threadLocal.set(Thread.currentThread().getName() + (Math.random() * 100D));
        }
        System.out.println(threadLocal.get());
    }
}

多次运行返回结果

main22.761071473890006
main22.761071473890006
Thread-056.212406593371476
main22.761071473890006
Thread-113.707351108894805

结果分析:同一个线程取出来的值是相同的，而且在多个线程运行过程中不会覆盖其他线程存放的数据

表明，ThreadLocal，它是线程绑定的变量，提供线程局部变量（一个线程一个ThreadLocal，A线程的ThreadLocal只能看到A线程的ThreadLocal，不能看到B线程的ThreadLocal）