问题发现

先看一段代码：

public class ThreadLocalTest {
    public static void main(String[] args) {
         SynchronizedTest synchronizedTest = new SynchronizedTest();
        Thread thread1 = new Thread(()->synchronizedTest.sync1());
        System.out.println("thread1-define");
        Thread thread2 = new Thread(()->synchronizedTest.sync2());
        System.out.println("thread2-define");
        thread1.run();
        System.out.println("thread1-run");
        thread2.run();
        System.out.println("thread2-run");
    }
}

public class SynchronizedTest {

    public  void sync1() {
        while (true) {

        }
    }

    public void sync2() {
        System.out.println("HAHA");
    }
}

执行结果：

thread1-define
thread2-define

然后进程就死循环了

问题分析

java中thread的start()和run()的区别：

1. start() 方法来启动线程，真正实现了多线程运行，这时无需等待run方法体代码执行完毕而直接继续执行下面的代码。

2. run() 方法当作普通方法的方式调用，程序还是要顺序执行，还是要等待run方法体执行完毕后才可继续执行下面的代码。
   Thread的源码如下：

/**
     * If this thread was constructed using a separate
     * <code>Runnable</code> run object, then that
     * <code>Runnable</code> object's <code>run</code> method is called;
     * otherwise, this method does nothing and returns.
     * <p>
     * Subclasses of <code>Thread</code> should override this method.
     *
     * @see     #start()
     * @see     #stop()
     * @see     #Thread(ThreadGroup, Runnable, String)
     */
    @Override
    public void run() {
        if (target != null) {
            target.run();
        }
    }

所以直接调用run方法并没有启动线程！
所以直接调用run方法并没有启动线程！
所以直接调用run方法并没有启动线程！

解决方案

改成如下代码：

public class ThreadLocalTest {
    public static void main(String[] args) {
         SynchronizedTest synchronizedTest = new SynchronizedTest();
        Thread thread1 = new Thread(()->synchronizedTest.sync1());
        System.out.println("thread1-define");
        Thread thread2 = new Thread(()->synchronizedTest.sync2());
        System.out.println("thread2-define");
        thread1.start();
        System.out.println("thread1-run");
        thread2.start();
        System.out.println("thread2-run");
    }
}

public class SynchronizedTest {

    public  void sync1() {
        while (true) {

        }
    }

    public void sync2() {
        System.out.println("HAHA");
    }
}

线程就能正常启动了，执行结果如下：

thread1-define
thread2-define
thread1-run
thread2-run
HAHA