萌新问一个java多线程同步死锁的问题

Question

下面这两段代码,一个实现Runnable接口,一个继承Thread类,前面的能正常交替输出
但是后面继承Thread的运行会死锁,没想明白为什么会死锁,求指教

public class Test3 {
       static  class MyRun implements Runnable {
            static int i = 0;
            @Override
            public synchronized  void run() {
                for (int j = 0; j < 10; j++) {
                    if(i%2==0)
                        System.out.println(Thread.currentThread().getName()+":A");
                    else
                        System.out.println(Thread.currentThread().getName()+":B");
                    i++;
                    this.notifyAll();
                    try {
                        if(i>=19)
                            Thread.sleep(10);
                        else
                            this.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }

        public static void main(String[] args) {
            MyRun myRun = new MyRun();
            Thread a = new Thread(myRun);
            Thread b = new Thread(myRun);
            a.start();
            b.start();
        }
    }

public class Test3 {
       static  class MyRun extends Thread {
            static int i = 0;
            @Override
            public synchronized  void run() {
                for (int j = 0; j < 10; j++) {
                    if(i%2==0)
                        System.out.println(Thread.currentThread().getName()+":A");
                    else
                        System.out.println(Thread.currentThread().getName()+":B");
                    i++;
                    this.notifyAll();
                    try {
                        if(i>=19)
                            Thread.sleep(10);
                        else
                            this.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }

        public static void main(String[] args) {
            MyRun m1 = new MyRun();
            MyRun m2 = new MyRun();
            m1.start();
            m2.start();
        }
    }

Answer 1

int i = 0;移到run方法中试试，去掉static