java中多线程同步问题求大神指教

class Counter extends Thread{
private Result res;
    public Counter(String name,Result res){
        super(name);
        this.res=res;
}
    @Override
    public void run() {
    try {
        sleep(1000);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
    e.printStackTrace();
}
        int sum=0;
        for(int i=1;i<=100;i++){
           sum+=i;
       }
    res.set(sum);
    while(!res.getFlag()){//判断那个打印的是否在等；
    try {
        sleep(100);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}
    synchronized (res) {
        res.notifyAll();
    }
    System.out.println(getName()+"set num end...");
    }
}
//print
class Printer extends Thread{
    private Result res;
    public Printer(String name,Result res){
        super(name);
        this.res=res;
    }
    @Override
    public void run() {
        synchronized (res) {
            if(!res.getFlag()){
                res.setFlag(true);
        try {
            this.wait();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}
    System.out.println(getName()+" get res:"+res.get());
    }
}
public class CalcaterTest {
    public static void main(String[] args) {
        System.out.println("main begin...");
        Result r=new Result();
        Counter c=new Counter("cal:", r);
        Printer p=new Printer("print:", r);
        c.start();
        p.start();
        System.out.println("main eend..");
    }
}