Java多线程synchronized、wait和notify问题

Question

废话不多说，直接粘测试代码

public class Test{
    public static void main(String[] args) {
        try {
            ThreadB tb = new ThreadB();
            tb.start();
            System.out.println("0");
            synchronized (tb) {
                System.out.println("3");
                tb.wait();
                System.out.println("4");
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

public class ThreadB extends Thread {

    @Override
    public void run() {
        synchronized (this) {
            System.out.println("1");
            notify();
            System.out.println("2");
        }
    }

}

为什么输出结果
有时候是：
0
1
2
3
有时候是：
0
1
2
3
4

Answer 1

public class Test{ public static void main(String[] args) { try { ThreadB tb =...