你需要实现一个高效的缓存，它允许多个用户读，但只允许一个用户写，以此来保持它的完整性，你会怎样去实现它？

 Lock读写锁机制可以实现！ 

在Java中Lock接口比synchronized块的优势是什么？

 Lock接口最大的优势是为读和写分别提供了锁。

 1 import java.text.SimpleDateFormat;
 2 import java.util.Date;
 3 import java.util.Random;
 4 import java.util.concurrent.locks.ReadWriteLock;
 5 import java.util.concurrent.locks.ReentrantReadWriteLock;
 6 
 7 
 8 
 9 
10 public class JoinTest2 {    
11   
12     public static void main(String[] args) {  
13         final TheData theData = new TheData();
14         for(int i=0;i<4;i++){
15             new Thread(new Runnable() {
16                 @Override
17                 public void run() {
18                     theData.get();
19                 }
20             }).start();
21         }
22         for(int i=0;i<4;i++){
23             new Thread(new Runnable() {
24                 @Override
25                 public void run() {
26                     theData.put(new Random().nextInt(1000));
27                 }
28             }).start();
29         }        
30     }  
31     
32 
33 } 
34 
35 class  TheData{
36     private Integer data = 0;
37     private ReadWriteLock rwLock = new ReentrantReadWriteLock();
38     SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
39     public void get(){
40         rwLock.readLock().lock();//读锁开启，读进程均可进入
41         try{//用try finally来防止因异常而造成的死锁
42             System.out.println(Thread.currentThread().getName()+"read lock is ready.."+sdf.format(new Date()));
43             Thread.sleep(1000);
44             System.out.println(Thread.currentThread().getName()+"read data is"+data);
45         }catch (InterruptedException e) {
46             e.printStackTrace();
47         }finally{
48             rwLock.readLock().unlock();//读锁解锁
49         }
50     }
51     
52     public void put(Integer data){
53         rwLock.writeLock().lock();//写锁开启，这时只有一个写线程进入
54         try{//用try finally来防止因异常而造成的死锁
55             System.out.println(Thread.currentThread().getName()+"write lock is ready.."+sdf.format(new Date()));
56             Thread.sleep(1000);
57             this.data = data;
58             System.out.println(Thread.currentThread().getName()+"write data is"+data);                
59 
60         }catch (InterruptedException e) {
61             e.printStackTrace();
62         }finally{
63             rwLock.writeLock().unlock();//写锁解锁
64         }
65     }
66 }

运行结果如下：