java 张三和李四的死锁

class ZhangSan{
    public void say(){
        System.out.println("Zhang said:you should lend your painting to me!");
    }
    public void get(){
        System.out.println("Zhang has got it!");
    }
}
class LiSi{
    public void say(){
        System.out.println("Li said:you should lend your book to me!");
    }
    public void get(){
        System.out.println("Li has got it!");
    }
}
public class DeadLock implements Runnable{
    private static ZhangSan zs=new ZhangSan();
    private static LiSi ls=new LiSi();
    private boolean flag=false;
    public void run(){
        if(flag){
            synchronized (zs){
                zs.say();
                try{
                    Thread.sleep(500);
                }catch (InterruptedException e){
                    e.printStackTrace();
                }
                synchronized (ls){
                    zs.get();
                }
            }
        }else{
             synchronized (ls){
                 ls.say();
                 try{
                     Thread.sleep(500);
                 }catch (InterruptedException e){
                     e.printStackTrace();
                 }
                 synchronized (zs){
                     ls.get();
                 }
             }
        }
    }
    public static void main(String[] args) {
        DeadLock t1=new DeadLock();
        DeadLock t2=new DeadLock();
        t1.flag=true;
        t2.flag=false;
        Thread thA=new Thread(t1);
        Thread thB=new Thread(t2);
        thA.start();
        thB.start();
    }
}

从程序中可以看出，两个线程都在等待彼此执行完成，从而死锁。。