观察者模式

public class Subject {
    
    private int data;
    
    private boolean isChange;

    private Set<Observer> observers=new HashSet<Observer>();
    
    public void register(Observer obj){
        observers.add(obj);
    }
    
    public void remove(Observer obj){
        observers.remove(obj);
    }
    
    public  void notifyAlls(){
        if(isChange){
            for(Observer ob:observers){
                ob.call(data);
            }
            isChange=false;
        }
    }
    
    public  void setData(int data){
        if(data!=this.data)isChange=true;
        this.data=data;
    }
}

public interface Observer {
    public abstract void call(int data);
}

public class Jack implements Observer{

    @Override
    public void call(int data) {
        System.out.println("Jack:"+data);
        
    }

}

public class Rusy implements Observer{

    @Override
    public void call(int data) {
        System.out.println("Rusy:"+data);
    }

}