Java多线程-线程死锁问题

/**
 * 演示线程的死锁问题
 * 死锁的理解：不同的线程分别占用对方需要的同步资源不放弃，都在等待对方放弃自己需要的同步资源，就形成了死锁
 * @author orz
 */
public class ThreadTest {
    public static void main(String[] args) {
        StringBuffer s1=new StringBuffer();
        StringBuffer s2=new StringBuffer();
        new Thread(){
            @Override
            public void run() {
                synchronized (s1)
                {

                    s1.append("a");
                    s2.append("1");
                    try
                    {
                        Thread.sleep(100);
                    } catch (Exception e)
                    {
                        e.printStackTrace();
                    }

                    synchronized (s2)
                    {
                        s1.append("b");
                        s2.append("2");
                        System.out.println(s1);
                        System.out.println(s2);
                    }
                }
            }
        }.start();

        new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (s2)
                {
                    s1.append("c");
                    s2.append("3");
                    try
                    {
                        Thread.sleep(100);
                    } catch (Exception e)
                    {
                        e.printStackTrace();
                    }
                    synchronized (s1)
                    {
                        s1.append("d");
                        s2.append("4");
                        System.out.println(s1);
                        System.out.println(s2);
                    }
                }
            }
        }).start();
    }

}