static ThreadLocal<String> stringThreadLocal = new ThreadLocal<>();

@Test

public  void test01(){

    Thread thread1 = new Thread(){

        @Override

        public void run() {

         stringThreadLocal.set("threadName===>"+Thread.currentThread().getName());

            System.out.println(this.getName()+" thread get the value:"+stringThreadLocal.get());

        }

    };

    Thread thread2 = new Thread(){

        @Override

        public void run() {

         stringThreadLocal.set("threadName===>"+Thread.currentThread().getName());

            System.out.println(this.getName()+" thread get the value:"+stringThreadLocal.get());

        }

    };

    Thread thread3 = new Thread(){

        @Override

        public void run() {

         stringThreadLocal.set("threadName===>"+Thread.currentThread().getName());

            System.out.println(this.getName()+" thread get the value:"+stringThreadLocal.get());

        }

    };

    thread1.start();

    thread2.start();

    thread3.start();

    System.out.println("main线程调用set方法之前："+stringThreadLocal.get());

    stringThreadLocal.set("main 线程set的值");

    System.out.println("main线程调用set方法之后："+stringThreadLocal.get());

}