java design pattern - observer pattern

王银批评Gang Of 4 和他们搞出来的Design pattern， 迷信design pattern 是没用的，看看还是可以的。
Java 确实是复杂的玩意，写起来太复杂了，看代码又找不到真正干活的代码在哪里，缺少了多重继承，搞出来一个interface. 

any way ，贴一个design pattern, 印度人写的 出自Java Design Patterns 一书.

1个observer 对应 1个subject 

package ObserverPattern;

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

class Observer{
    public void update(){
        System.out.println("flag value changed in Subject");
    }
}

interface ISubject{
    void register(Observer o);
    void unregister(Observer o);
    void notifyObservers();
}

class Subject implements ISubject {
    List<Observer> observerList=new ArrayList<Observer>();
    private int _flag;

    public int getFlag(){
        return _flag;
    }

    public void setFlag(int _flag){
        this._flag=_flag;
        //flag value changed, so notify observer(s)
        notifyObservers();
        }

    @Override
    public void register(Observer o){
        observerList.add(o);
    }

    @Override
    public void unregister(Observer o){
        observerList.remove(o);
    }

    @Override
    public void notifyObservers(){
        for(int i=0;i<observerList.size();i++){
            observerList.get(i).update();
        }
    }
}

class ObserverPatternEX{
    public static void main(String[] args){
        System.out.println("****Observer pattern Demo***");
        Observer o1=new Observer();
        Subject sub1=new Subject();

        sub1.register(o1);
        System.out.println("Setting flag = 5");
        sub1.setFlag(5);
        System.out.println("Setting flag = 125");
        sub1.setFlag(125);
        sub1.unregister(o1);
        //No notification this time to o1, since it is unregistered
        System.out.println("Setting flag=50");
        sub1.setFlag(50);
    }
    }

对个Observer对应一个subject 

package ObserverPattern2;

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

interface IObserver{
    void update(int i);
}

class Observer1 implements IObserver{
    @Override
    public void update(int i){
        System.out.println("Observer1: myValue in Subject is now: "+i);
    }
}

class Observer2 implements IObserver{
    @Override
    public void update(int i){
        System.out.println("Observer2: observers->myValue is changed in Subject to: "+i);
    }
}

interface ISubject{
    void register(IObserver o);
    void unregister(IObserver o);
    void notifyObservers(int i);
}


class Subject implements ISubject{
    private int myValue;
    List<IObserver> observersList = new ArrayList<IObserver>();

    public int getMyValue() {
        return myValue;
    }

    public void setMyValue(int myValue) {
        this.myValue = myValue;
        notifyObservers(myValue);
    }

    @Override
    public void register(IObserver o){
        observersList.add(o);
    }

    @Override
    public void unregister(IObserver o){
        observersList.remove(o);
    }

    @Override
    public void notifyObservers(int updatedValue){
        for(int i=0;i<observersList.size();i++){
            observersList.get(i).update(updatedValue);
        }
    }
}

class ObserverPatternModified{
    public static void main(String[] args){
        System.out.println("Modified Observer Pattern Demo");
        Subject sub = new Subject();
        Observer1 ob1 = new Observer1();
        Observer2 ob2 = new Observer2();

        sub.register(ob1);
        sub.register(ob2);

        sub.setMyValue(5);
        System.out.println();
        sub.setMyValue(25);
        System.out.println();

        //unregister ob1 only
        sub.unregister(ob1);
        //Now only ob2 will observer the change
        sub.setMyValue(100);

    }
}

最后是多个observer 对应多个subject 

package ObserverPattern3;

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

interface IObserver{
    void update(String s, int i);
}

class Observer1 implements IObserver{

    @Override
    public void update(String s, int i){
        System.out.println("Observer1: myValue "+s+" is now: "+i);

    }
}

class Observer2 implements IObserver{

    @Override
    public void update(String s, int i){
        System.out.println("Observer2: ->myValue is changing in "+s+" to : "+i);
    }
}

class Observer3 implements IObserver{

    @Override
    public void update(String s, int i){
        System.out.println("Observer3 is observing: myValue is changed in "+s+" to : "+i);
    }
}

interface ISubject{
    void register(IObserver o);
    void unregister(IObserver o);
    void notifyObservers(int i);
}

class Subject1 implements ISubject{
    private int myValue;
    List<IObserver> observersList=new ArrayList<IObserver>();

    public int getMyValue(){
        return myValue;
    }

    public void setMyValue(int myValue){
        this.myValue=myValue;
        notifyObservers(myValue);
    }

    @Override
    public void register(IObserver o){
        observersList.add(o);
    }

    @Override
    public void unregister(IObserver o){
        observersList.remove(o);
    }

    @Override
    public void notifyObservers(int updatedValue){
        for(int i=0;i<observersList.size();i++){
            observersList.get(i).update(this.getClass().getSimpleName(), updatedValue);
        }
    }
}

class Subject2 implements ISubject{
    private int myValue;
    List<IObserver> observersList=new ArrayList<IObserver>();

    public int getMyValue(){
        return myValue;
    }

    public void setMyValue(int myValue){
        this.myValue=myValue;
        notifyObservers(myValue);
    }

    @Override
    public void register(IObserver o){
        observersList.add(o);
    }

    @Override
    public void unregister(IObserver o){
        observersList.remove(o);
    }

    @Override
    public void notifyObservers(int updatedValue){
        for(int i=0;i<observersList.size();i++){
            observersList.get(i).update(this.getClass().getSimpleName(), updatedValue);
        }
    }

}

class ObserverPatternEX3 {
    public static void main(String[] args){
        System.out.println("*** Observer Pattern Demo3***\n");
        Subject1 sub1 = new Subject1();
        Subject2 sub2 = new Subject2();

        Observer1 ob1 = new Observer1();
        Observer2 ob2 = new Observer2();
        Observer3 ob3 = new Observer3();

        //Observer1 and Observer2 registers to //subject 1
        sub1.register(ob1);
        sub1.register(ob2);

        //Observer2 and Observer3 registers to //subject 2
        sub2.register(ob2);
        sub2.register(ob3);

        //set new value to subject 1
        //observer1 and observer2 get //notification
        sub1.setMyValue(50);
        System.out.println();
        //Set new value to Subject 2
        //Observer2 and Observer3 get //notification
        sub2.setMyValue(250);
        System.out.println();
        //unregister Observer2 from subject 1
        sub1.unregister(ob2);

        //set new value to subject & only //observer 1 is notified
        sub1.setMyValue(550);
        System.out.println();
        //ob2 can still notice change in //subject 2
        sub2.setMyValue(750);
    }
}