这段java代码有什么错误。这样写有什么不好。题目的意图是为了测试wait() notify()

public class Thread_waiting {
public static void main(String[] args){
Methods m=new Methods();
new ThreadAB().start();
new ThreadC().start();
}

}
class Methods{
int flag=1;
boolean available=false;
public synchronized void fun1(){
if(available)
try{wait();} catch(Exception e){}
if(flag==1){
System.out.println("...Start.");
flag=2;
}
if(flag==3){
System.out.println("...End.");
flag=4;
}
available=true;
notify();
}
public synchronized void fun2(){
if(!available)
try{wait();} catch(Exception e){}
if(flag==2) {available=false;flag=3;notifyAll();}
if(flag==4) System.out.println("线程C自己结束");
}
}
class ThreadAB extends Thread{
Methods m=null;

public void run(){
m.fun1();
}
}
class ThreadC extends Thread{
M