synchronized 和 static synchronized

挺简单的一个问题，今天被人问起了顺手写一下。

其实 synchronized 是实例对象锁，而 static 是类对象锁。每个类类对象在一个classloader只会有一个。

下面两段简单的代码就能验证

package lock;

import com.meta.mq.common.utils.ThreadUtil;

/**
 * @author : haifeng.pang.
 * @version 0.1 : Human v0.1 2021/1/28 下午5:48 By haifeng.pang.
 * @description :
 */
public class Human {

    public synchronized void say(String name) {
        System.out.println("say " + name);
        ThreadUtil.quietSleep(10000);
    }

    public synchronized void eat(String name) {
        System.out.println("eat " + name);
    }

    public static synchronized void sayStatic(String name) {
        System.out.println("static say" + name);
    }

    public static synchronized void eatStatic(String name) {
        System.out.println("static eat" + name);
        ThreadUtil.quietSleep(10000);
    }
}

package lock;

/**
 * @author : haifeng.pang.
 * @version 0.1 : Test v0.1 2021/1/28 下午5:49 By haifeng.pang.
 * @description :
 */
public class Test {


    @org.junit.Test
    public void test() {
        Human human = new Human();
        Human human1 = new Human();
        Thread threadA = new Thread(new Runnable() {
            @Override
            public void run() {
                human.say("im threadA");
            }
        });

        Thread threadB = new Thread(new Runnable() {
            @Override
            public void run() {
                human.eat("im threadB");

            }
        });

        threadA.start();

        threadB.start();

        try {
            threadA.join();
            threadB.join();
        }catch (Exception e) {
            //
        }


    }
}