Java面试--Synchronized和Lock区别

╰半橙微兮° 2021-09-27 07:12 402阅读 0赞

> **面试题：Synchronized和Lock区别(大疆面试题、网易笔试题)**

**一、Synchronized和Lock区别**  
![这里写图片描述][70]  
**二、Lock源码**

public interface Lock { 
        //获取锁，如果锁被暂用则一直等待
        void lock();
        //用该锁的获得方式，如果线程在获取锁的阶段进入了等待，那么可以中断此线程，先去做别的事 
        void lockInterruptibly() throws InterruptedException;
        //注意返回类型是boolean，如果获取锁的时候锁被占用就返回false，否则返回true
        boolean tryLock();
        //比起tryLock()就是给了一个时间期限，保证等待参数时间
        boolean tryLock(long time, TimeUnit unit) throws InterruptedException;
        //释放锁
        void unlock();
    }

下面是Lock一般使用的例子，注意ReentrantLock是Lock接口的实现：

import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    public class LockTest {
        private Lock lock = new ReentrantLock();
        //需要参与同步的方法
        private void method(Thread thread){
            lock.lock();
            try {
                System.out.println("线程名"+thread.getName() + "获得了锁");
            }catch(Exception e){
                e.printStackTrace();
            } finally {
                System.out.println("线程名"+thread.getName() + "释放了锁");
                lock.unlock();
            }
        }
    
        public static void main(String[] args) {
            LockTest lockTest = new LockTest();
            //线程1
            Thread t1 = new Thread(new Runnable() {
                @Override
                public void run() {
                    lockTest.method(Thread.currentThread());
                }
            }, "t1");
    
            Thread t2 = new Thread(new Runnable() {
                @Override
                public void run() {
                    lockTest.method(Thread.currentThread());
                }
            }, "t2");
    
            t1.start();
            t2.start();
        }
    }
    //运行结果
    //线程名t1获得了锁
    //线程名t1释放了锁
    //线程名t2获得了锁
    //线程名t2释放了锁

tryLock()方法:

package com.brickworkers;
    
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    public class LockTest {
        private Lock lock = new ReentrantLock();
    
        //需要参与同步的方法
        private void method(Thread thread){
            if(lock.tryLock()){
                try {
                    System.out.println("线程名"+thread.getName() + "获得了锁");
                }catch(Exception e){
                    e.printStackTrace();
                } finally {
                    System.out.println("线程名"+thread.getName() + "释放了锁");
                    lock.unlock();
                }
            }else{
                System.out.println("我是"+Thread.currentThread().getName()+"有人占着锁，我就不要啦");
            }
        }
    
        public static void main(String[] args) {
            LockTest lockTest = new LockTest();
            //线程1
            Thread t1 = new Thread(new Runnable() {
                @Override
                public void run() {
                    lockTest.method(Thread.currentThread());
                }
            }, "t1");
    
            Thread t2 = new Thread(new Runnable() {
                @Override
                public void run() {
                    lockTest.method(Thread.currentThread());
                }
            }, "t2");
    
            t1.start();
            t2.start();
        }
    }
    //运行结果：
    //线程名t2获得了锁
    //我是t1有人占着锁，我就不要啦
    //线程名t2释放了锁

Lock中可以自己控制锁是否公平，而且，默认的是非公平锁，以下是ReentrantLock的构造函数：

public ReentrantLock() {
            sync = new NonfairSync();//默认非公平锁
    }

> **转载请标明出处，原文地址：[https://blog.csdn.net/weixin\_41835916][https_blog.csdn.net_weixin_41835916] 如果觉得本文对您有帮助，请点击顶支持一下，您的支持是我写作最大的动力，谢谢。  
> ![这里写图片描述][70 1]**

[70]: /images/20210923/d0327d25d7704b5e9cf27ed7255cacd0.png
[https_blog.csdn.net_weixin_41835916]: https://blog.csdn.net/weixin_41835916
[70 1]: /images/20210923/b6f82eb7fd4e4a17b62c75594ce421fb.png