多线程先输出2再输出1

wait/notify

package com.kang.multithread;

/**
 * @author klr
 * @create 2020-09-16-10:53
 */
public class Print21 {

    static final Object lock = new Object();
    static boolean con = false;

    public static void main(String[] args) {
        new Thread(()->{
            synchronized (lock) {
                while (!con) {
                    try {
                        lock.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                System.out.println(1);
            }

        },"t1").start();

        new Thread(()->{
            synchronized (lock) {
                System.out.println(2);
                con = true;
                lock.notify();
            }
        },"t2").start();
    }
}

park/unpark

package com.kang.multithread;

import java.util.concurrent.locks.LockSupport;

/**
 * @author klr
 * @create 2020-09-16-10:53
 */
public class Print21 {

    static final Object lock = new Object();
    static boolean con = false;

    public static void main(String[] args) {
        Thread t1 = new Thread(() -> {
//            synchronized (lock) {
//                while (!con) {
//                    try {
//                        lock.wait();
//                    } catch (InterruptedException e) {
//                        e.printStackTrace();
//                    }
//                }
            LockSupport.park();
            System.out.println(1);
//            }

        }, "t1");
        t1.start();

        new Thread(()->{
//            synchronized (lock) {
//                System.out.println(2);
//                con = true;
//                lock.notify();
//            }
            System.out.println(2);
            LockSupport.unpark(t1);
        },"t2").start();
    }
}