Error:This method must return a result of type String?

[沈家大帅]

路过的高手顺便指点下我啊
先行谢过
求解Error:This method must return a result of type String

public class WaitNotifyDemo {

	/**
	 * @param args
	 */
	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		MessageBoard m = new MessageBoard();//构造共享的信息板类对象
		Reader readfrom_m = new Reader(m);
		Writer writeto_m = new Writer(m);
		readfrom_m.start();
		writeto_m.start();
	}

}
class MessageBoard {                 //共享的信息板
	private String message;
	private boolean ready = false;
	public synchronized String read(){ //ERROR
		while(ready == false){
			try{
				wait();
			}catch(InterruptedException e){}
			ready = false;
			notify();
			return message;
		}
		
	}
	public synchronized void write(String s) {
		while(ready == true){
			try{
				wait();
			}catch(InterruptedException e){}
			message = s;
			ready = true;
			notify();
		}
		
	}
}
class Reader extends Thread{    //定义读线程类
	private MessageBoard mBoard;
	public Reader(MessageBoard m){
		mBoard = m;
	}
	public void run(){
		String s = "";
		boolean reading = true;
		while(reading){
			s = mBoard.read();
			System.out.println("Reader read:"+s);
			if(s.equals("logoff"))
				reading = false;
			}
		System.out.println("Finished: 10 seconds...");
		try{
			sleep(10000);
		}catch(InterruptedException e){}
	}
}
class Writer extends Thread{   // 定义写线程类
	private MessageBoard mBoard;
	private String messages[] = {
			"Monday  :--------","....","Sunday  : --------"
	};
	public Writer(MessageBoard m){
		mBoard = m;
		
	}
	public void run(){
		for(int i=0;i<messages.length;i++){
			mBoard.write(messages[i]);
			System.out.println("Writer wrote:"+messages[i]);
			try{
				sleep((int)(Math.random()*100));		
			}catch(InterruptedException e){}
		}
		mBoard.write("logoff");
	}
}

[zz578]

read有可能执行不了return语句，必须考虑到这种情况并返回适当值。

[xiaohuanjie]

public synchronized String read(){ //ERROR
while(ready == false){
try{
wait();
}catch(InterruptedException e){}
ready = false;
notify();
return message;
}

}

没有返回值（String），

你的这个方法的意思是只在catch到异常的时候才会return message，

如果没有异常，就不会 return一个String，这显然是不对的，

没有catch到异常也应该有返回值

public synchronized String read(){ //ERROR
while(ready == false){
try{
wait();
}catch(InterruptedException e){}
ready = false;
notify();
return message;
}
return something;
}

[xiaohuanjie]

对不起，我看错了

应该是catch到异常的时候也应该有返回值

惭愧........

[沈家大帅]

[Quote=引用 1 楼 zz578 的回复:]
read有可能执行不了return语句，必须考虑到这种情况并返回适当值。
[/Quote]
明白了， while外没有return。谢谢

[沈家大帅]

[Quote=引用 3 楼 xiaohuanjie 的回复:]
应该是catch到异常的时候也应该有返回值
[/Quote]
捕获到异常，因为无处理继续会执行下面语句
return message;
同样谢谢啦