synchronized 关键字测试

1. 对象上有关键字

package com.study.juc.sync;

import java.util.concurrent.TimeUnit;

public class Test1 {

    public static void main(String[] args) throws InterruptedException {
        Phone phone = new Phone();
        Thread t1= new Thread(()->{
            try {
                phone.sendSms();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        },"A");
        t1.start();

        TimeUnit.SECONDS.sleep(1);

        Thread t2=new Thread(()->{
            phone.call();
        },"B");

        t2.start();

        Thread t3=new Thread(()->{
            phone.hello();
        },"c");

        t3.start();
    }

}

class Phone{

    public synchronized void call(){
        System.out.println("打电话");
    }

    public synchronized void sendSms() throws InterruptedException {
        TimeUnit.SECONDS.sleep(4);
        System.out.println("发短信");
    }

    public void hello(){
        System.out.println("hello ");
    }
}

请输出上面例子的结果。

• 结论
  
  如果时同一个对象上，加 synchronized 那么这个对象的一个方法先进入，另外的方法只能等待，需要登台获取锁的对象完成才能执行。
  
  如果方法上没有锁，那么不会等待。

1. 两个对象的调用

package com.study.juc.sync;

import java.util.concurrent.TimeUnit;

public class Test2 {

    public static void main(String[] args) throws InterruptedException {
        Phone2 phone1 = new Phone2();
        Phone2 phone2 = new Phone2();
        Thread t1= new Thread(()->{
            try {
                phone1.sendSms();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        },"A");
        t1.start();

        TimeUnit.SECONDS.sleep(1);

        Thread t2=new Thread(()->{
            phone2.call();
        },"B");

        t2.start();

    }

}

class Phone2{

    public synchronized void call(){
        System.out.println("打电话");
    }

    public synchronized void sendSms() throws InterruptedException {
        TimeUnit.SECONDS.sleep(4);
        System.out.println("发短信");
    }

    public void hello(){
        System.out.println("hello ");
    }
}

创建两个对象，分别调用其方法，由于是两个对象，锁的作用范围也是对象，因此两个对象的锁不互相干扰。

1. 静态方法

package com.study.juc.sync;

import java.util.concurrent.TimeUnit;

public class Test3 {

    public static void main(String[] args) throws InterruptedException {

        Phone3 phone1 = new Phone3();
        Phone3 phone2 = new Phone3();
        Thread t1= new Thread(()->{
            try {
                phone1.sendSms();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        },"A");
        t1.start();

        TimeUnit.SECONDS.sleep(1);

        Thread t2=new Thread(()->{
            phone2.call();
        },"B");

        t2.start();
    }
}

class Phone3{

    public static synchronized void call(){
        System.out.println("打电话");
    }

    public static synchronized void sendSms() throws InterruptedException {
        TimeUnit.SECONDS.sleep(4);
        System.out.println("发短信");
    }

}

synchronized 作用在 class 上，所以锁的对象是 class。

1. 一个实例方法，一个类方法

package com.study.juc.sync;

import java.util.concurrent.TimeUnit;

public class Test4 {

    public static void main(String[] args) throws InterruptedException {

        Phone4 phone = new Phone4();
        Thread t1= new Thread(()->{
            try {
                phone.sendSms();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        },"A");
        t1.start();

        TimeUnit.SECONDS.sleep(1);

        Thread t2=new Thread(()->{
            phone.call();
        },"B");

        t2.start();

    }

}

class Phone4{

    public  synchronized void call(){
        System.out.println("打电话");
    }

    public static synchronized void sendSms() throws InterruptedException {
        TimeUnit.SECONDS.sleep(4);
        System.out.println("发短信");
    }

}

一个调用静态方法，一个调用实例方法，实际是两把锁相互不影响。