Lock与synchronized的异同

主要相同点：Lock能完成synchronized所实现的所有功能

主要不同点：Lock有比synchronized更精确的线程语义和更好的性能。synchronized会自动释放锁，而Lock一定要求程序员手工释放，并且必须在finally从句中释放。Lock还有更强大的功能，例如，它的tryLock方法可以非阻塞方式去拿锁。

举例说明（对下面的题用lock进行了改写）：

package com.huawei.interview;

 

import java.util.concurrent.locks.Lock;

import java.util.concurrent.locks.ReentrantLock;

 

public class ThreadTest {

 

     /**

      * @param args

      */

    

     private int j;

     private Lock lock = new ReentrantLock();

     public static void main(String[] args) {

          // TODO Auto-generated method stub

          ThreadTest tt = new ThreadTest();

          for(int i=0;i<2;i++)

          {

              new Thread(tt.new Adder()).start();

              new Thread(tt.new Subtractor()).start();

          }

     }

 

     private class Subtractor implements Runnable

     {

 

          @Override

          public void run() {

              // TODO Auto-generated method stub

              while(true)

              {

                   /*synchronized (ThreadTest.this) {             

                        System.out.println("j--=" + j--);

                        //这里抛异常了，锁能释放吗？

                   }*/

                   lock.lock();

                   try

                   {

                        System.out.println("j--=" + j--);

                   }finally

                   {

                        lock.unlock();

                   }

              }

          }

         

     }

    

     private class Adder implements Runnable

     {

 

          @Override

          public void run() {

              // TODO Auto-generated method stub

              while(true)

              {

                   /*synchronized (ThreadTest.this) {

                   System.out.println("j++=" + j++);

                   }*/

                   lock.lock();

                   try

                   {

                        System.out.println("j++=" + j++);

                   }finally

                   {

                        lock.unlock();

                   }                 

              }            

          }

         

     }