代码如下：

import static java.lang.System.out;

/**
 * 交替打印奇偶数
 *
 * @author ***
 * @create 2018-11-13 19:48
 */
public class Test0001 {
    public static Object OBJ = new Object();
    public static int i;

    public static class MyThread1 extends Thread {
        @Override
        public void run() {
            while( true ) {
                synchronized( OBJ ) {
                    out.println(Thread.currentThread().getName() + "  enter----  " + i);
                    if( i % 2 == 0 ) {
                        out.println(Thread.currentThread().getName() + "    " + i++);
                        try {
                            out.println(Thread.currentThread().getName() + "    wait");
                            OBJ.wait();
                            out.println(Thread.currentThread().getName() + "    wait over");
                        } catch( InterruptedException e ) {
                            e.printStackTrace();
                        }
                    } else {
                        out.println(Thread.currentThread().getName() + "    notify");
                        OBJ.notify();
                    }
                    out.println(Thread.currentThread().getName() + "leave---      " + i);
                }
            }
        }
    }

    public static class MyThread2 extends Thread {
        @Override
        public void run() {

            while( true ) {
                synchronized( OBJ ) {
                    out.println(Thread.currentThread().getName() + "  enter----  " + i);
                    if( i % 2 == 1 ) {
                        out.println(Thread.currentThread().getName() + "    " + i++);
                        out.println(Thread.currentThread().getName() + "    notify");
                        OBJ.notify();
                    } else {
                        try {
                            out.println(Thread.currentThread().getName() + "    wait");
                            OBJ.wait();
                            out.println(Thread.currentThread().getName() + "    wait over");
                        } catch( InterruptedException e ) {
                            e.printStackTrace();
                        }
                    }
                    out.println(Thread.currentThread().getName() + "leave---      " + i);
                }
            }
        }
    }

    public static void main( String[] args ) {
        Thread t1 = new MyThread1();
        Thread t2 = new MyThread2();
        t1.start();

        try {
            Thread.sleep(111);
        } catch( InterruptedException e ) {
            e.printStackTrace();
        }
        t2.start();
    }
}

执行结果如下：

Thread-0  enter----  0
Thread-0    0
Thread-0    wait
Thread-1  enter----  1
Thread-1    1
Thread-1    notify
Thread-1leave---      2    //语句1
Thread-1  enter----  2     //语句2
Thread-1    wait
Thread-0    wait over
Thread-0leave---      2
Thread-0  enter----  2
Thread-0    2
Thread-0    wait

然后程序就卡住了····
好奇的是，为什么 Thread-1 leave(语句1) 之后 Thread-1 又立马 enter(语句2) 了，按道理 Thread-1 leave之后不是应该 Thread-0 enter吗。。。求赐教!!