import java.text.SimpleDateFormat;import java.util.Date;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReadWriteLock;import java.util.concurrent.locks.ReentrantReadWriteLock;public class Data {	SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");    public  synchronized void  set(){		System.out.println(Thread.currentThread().hashCode() + "set:begin" + sdf.format(new Date()));	    try{	    	Thread.sleep(5000);	    }catch(Exception e){	    		    }finally{    		System.out.println(Thread.currentThread().hashCode() + "set:end" +sdf.format(new Date()));	    }	}		public synchronized void get(){		System.out.println(Thread.currentThread().hashCode() + "set:begin" + sdf.format(new Date()));	    try{	    	Thread.sleep(5000);	    }catch(Exception e){	    		    }finally{    		System.out.println(Thread.currentThread().hashCode() + "set:end" +sdf.format(new Date()));	    }	}}

　　

public class Worker extends Thread {	Data data;	boolean read;	public Worker(Data data, boolean read) {		this.data = data;		this.read = read;	}	public void run() {		if (read)			data.get();		else			data.set();	}}

　　

public class ReadWriteLockDemo {	public static void main(String args[]) {		Data data = new Data();		Worker thread1 = new Worker(data, true);		Worker thread2 = new Worker(data, true);		thread1.start();		thread2.start();	}}

　　

上面的代码使用synchronized锁，用synchronized修饰的方法只能同时被一个线程访问，于是代码中两个线程要依次执行，结果如下

8637543set:begin2015-03-22 10:35:26

8637543set:end2015-03-22 10:35:31

22474382set:begin2015-03-22 10:35:31

22474382set:end2015-03-22 10:35:36

 

下面使用读写锁，只需要修改Data类就可以了

import java.text.SimpleDateFormat;import java.util.Date;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReadWriteLock;import java.util.concurrent.locks.ReentrantReadWriteLock;public class Data {	SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");	ReadWriteLock lock = new ReentrantReadWriteLock();	Lock read = lock.readLock();	Lock write = lock.writeLock();    public  void  set(){		write.lock();		System.out.println(Thread.currentThread().hashCode() + "set:begin" + sdf.format(new Date()));	    try{	    	Thread.sleep(5000);	    }catch(Exception e){	    		    }finally{    		System.out.println(Thread.currentThread().hashCode() + "set:end" +sdf.format(new Date()));    	    write.unlock();	    }	}		public void get(){
    　　　　　　　　　read.lock()		System.out.println(Thread.currentThread().hashCode() + "set:begin" + sdf.format(new Date()));	    try{	    	Thread.sleep(5000);	    }catch(Exception e){	    		    }finally{    		System.out.println(Thread.currentThread().hashCode() + "set:end" +sdf.format(new Date())); 　　　　　　　　　 read.unlock()	    }	}}

同时读，结果

30771886set:begin2015-03-22 10:51:18

14718739set:begin2015-03-22 10:51:18

30771886set:end2015-03-22 10:51:23

14718739set:end2015-03-22 10:51:23

两个线程同时读取数据，同时执行结束，没有限制。

public class ReadWriteLockDemo {	public static void main(String args[]) {		Data data = new Data();		Worker thread1 = new Worker(data, false);		Worker thread2 = new Worker(data, true);		thread1.start();		thread2.start();	}}

　　第一个线程写， 第二个线程读

8637543set:begin2015-03-22 10:54:11

8637543set:end2015-03-22 10:54:16

4699264set:begin2015-03-22 10:54:16

4699264set:end2015-03-22 10:54:21

 

读写锁允许同时读，但不允许读写同时进行