关于java的wait()的有关问题

关于java的wait()的问题
首先请看代码：


package clone;

/**
 * 生产者与消费者的问题
 */
import java.util.*;
public class Run{
public static void main(String[]args){
Producer p = new Producer();
Consumer c = new Consumer();
new Thread(p,"p").start();//start时就会调用produce()
new Thread(c,"c").start();//start时就会调用consumption()
}
}

class Producer implements Runnable{
public Producer(){
if( null == goods ) goods = new ArrayList&lt;Goods&gt;();
}
@Override
public void run(){
try{
synchronized(Run.class){
if( 5 &gt; goods.size() )
for( int i=goods.size() ; i&lt;5 ; i++)
produce();
}
}
catch(Exception err){err.printStackTrace();}
}
public void produce() throws Exception{//生产
System.out.println("coming ! the current thread is "+Thread.currentThread().getName());
int size = goods.size()+1 ;
String name = String.valueOf(size);
goods.add(new Goods(size , name ,Double.parseDouble(name))) ;
}
private static List&lt;Goods&gt; goods;
public static List&lt;Goods&gt; obtainedGoods(){ 
System.out.println(Thread.currentThread().getName()+":"+goods.size());return goods ; }
}

class Consumer implements Runnable{
@Override
public void run(){
try{
synchronized(Run.class){
goods = Producer.obtainedGoods();
if( null == goods ) System.out.println(Thread.currentThread().getName()+":"+"do not have this kind of goods !");
if( 0 == goods.size() ) 
{
System.out.println(Thread.currentThread().getName()+":"+"this goods have been done not have ! we must wait for produce");
this.wait();
}
consumption();
this.notify();
}
}
catch(Exception err){
err = new IllegalMonitorStateException(Thread.currentThread().getName());
err.printStackTrace();
}
}
public void consumption() throws Exception{//消费
System.out.println("coming ! the current thread is "+Thread.currentThread().getName());
Goods g;
int i = goods.size() ;
while( 0 != i ){
g = (Goods)goods.get(i-1); 
 
g.displays();
i -- ;
}
}
private List&lt;Goods&gt; goods;
}

class Goods{//商品类
private int id ;
private String name = "goods";
private double price ;
public Goods(int id , String name , double price){this.id = id ; this.name = this.name+name ; this.price = price ;}
public void displays(){//显示商品
System.out.println(Thread.currentThread().getName()+":"+"id="+id+", name="+name+", price"+price);
}
}

以上代码会报错，报错说是：
java.lang.IllegalMonitorStateException: c
at clone.Consumer.run(Run.java:59)
at java.lang.Thread.run(Thread.java:619)

这个代码中，抛的异常也是我自定义的，比如上面报错中java.lang.IllegalMonitorStateException: c ，
这里的c 是发生异常时所运行的线程！！！

也就是说，在c线程运行时，发生了异常，这正是我自定义异常的目的！

--------------------------------------------
然而，问题却来了：
JDK1.6所述:
wait()、notify()必须：当前线程必须拥有此对象监视器
IllegalMonitorStateException - 如果当前线程不是此对象监视器的所有者。

我在Consumer类中写的wait()和notify()方法！线程c就是Consumer的对象c对应的那个线程！！！
那么，wait() notify()方法就应该是在本对象的监视器范围内！！！
既然如此，怎么会抛出IllegalMonitorStateException异常呢？

我初学多线程，求指教！
[解决办法]

public void run(){
        try{
            synchronized(Run.class){
                goods = Producer.obtainedGoods();
                if( null == goods ) System.out.println(Thread.currentThread().getName()+":"+"do not have this kind of goods !");
                if( 0 == goods.size() ) 
                {
                    System.out.println(Thread.currentThread().getName()+":"+"this goods have been done not have ! we must wait for produce"); 
 
                    this.wait();
                }
                consumption();
                this.notify();//这里抛异常
            }
        }
        catch(Exception err){
            err = new IllegalMonitorStateException(Thread.currentThread().getName());
            err.printStackTrace();
        }
    }

这里synchronize代码块的锁是Run.class（即所谓的监视器）
根据api，notify()的调用者就得是synchroize代码块的锁，不然就抛异常。这里要写成Run.class.notify()就行了。
或者上面的方法写成

public synchronized void run(){
try{
goods = Producer.obtainedGoods();
if( null == goods ) System.out.println(Thread.currentThread().getName()+":"+"do not have this kind of goods !");
if( 0 == goods.size() ) 
{
System.out.println(Thread.currentThread().getName()+":"+"this goods have been done not have ! we must wait for produce");
this.wait();
}
consumption();
this.notify();
}
catch(Exception err){
err = new IllegalMonitorStateException(Thread.currentThread().getName());
err.printStackTrace();
}

这杨写法是给方法上锁，默认锁是this。所以这里this.notify就不报错了
[解决办法]
虽然看不懂但是还是给你顶一下
[解决办法]
该回复于2013-08-21 08:40:30被管理员删除

关于java的wait()的有关问题

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