观察者模式

import java.util.List;
import java.util.ArrayList;

class Subject {
    private int state;
    private List<Observer> lists = new ArrayList<Observer>();

    public int getState() {
        return state;
    }

    public void setState(int state) {
        this.state = state;
        notifyAllObservers();
    }

    public void attach(Observer observer) {
        lists.add(observer);
    }

    public void notifyAllObservers() {
        for (Observer observer : lists) {
            observer.update();
        }
    }
}


abstract class Observer {
    protected Subject subject;
    abstract public void update();
}

class BinaryObserver extends Observer {
    public BinaryObserver(Subject subject) {
        this.subject = subject;
        this.subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println("Binary String: " + Integer.toBinaryString(subject.getState()));
    }
}

class OctalObserver extends Observer {
    public OctalObserver(Subject subject) {
        this.subject = subject;
        this.subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println("Octal String: " + Integer.toOctalString(subject.getState()));
    }
}

class HexObserver extends Observer {
    public HexObserver(Subject subject) {
        this.subject = subject;
        this.subject.attach(this);
    }

    @Override
    public void update() {
        System.out.println("Hexa String: " + Integer.toHexString(subject.getState()).toUpperCase());
    }
}



public class ObserverPatternDemo {
    public static void main(String args[]) {
        Subject subject = new Subject();

        Observer binaryObserver = new BinaryObserver(subject);
        Observer octalObserver = new OctalObserver(subject);
        Observer hexObserver = new HexObserver(subject);

        subject.setState(10);

        subject.setState(20);
    }
}