Java 觀察者模式

UML 模型如下

撰寫一個抽象類別Observer 有其抽象方法update.

package observer_pattern;

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

撰寫一個Subject類別 , 有加上觀察者跟移除觀察者的方法，還有一個notity 更新的方法

package observer_pattern;

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

public class Subject {
    List<Observer> observers;
    public Subject(){
        observers = new ArrayList<>();

    }

    public void add_observer(Observer observer){
        observers.add(observer);
    }
    public void remove_observer(Observer observer){
        observers.remove(observer);
    }

    public void notify_all(){
        for (Observer o:observers ) {
            o.update(this);
        }
    }
}

建立一個工廠模式FactoryMode繼承Subject，製程透過setPoint更新目前的品質，並呼叫notify_all 更新

public class FactoryMode extends Subject{
    float point;
    public FactoryMode(float point){
        super();
        this.point = point;
    }

    public float getPoint(){return this.point;}

    public void  setPoint(float point){
        this.point = point;
        this.notify_all();
    }
}

CheckPoitnt類別繼承抽象類別Observer，並實做update方法，產品品質介於上下管制界線時，呈現in spec

public class CheckPoint extends Observer{
    float ucl;
    float lcl;

    public CheckPoint(float ucl, float lcl){
        this.ucl = ucl;
        this.lcl = lcl;
    }

    @Override
    public void update(Subject subject) {
            FactoryMode fm =  (FactoryMode) subject;
            if (ucl>fm.getPoint() && lcl<fm.getPoint())
                System.out.printf("%.2f %.2f %.2f in spec\n",ucl,fm.point,lcl);
            else
                System.out.printf("%.2f %.2f %.2f out spec\n",ucl,fm.point,lcl);
    }
}

執行時，另用FactoryMode產生現在的點，並加上checkpoint。FactoryMode 透過setPoint 不斷生成製程。同時也更新

package observer_pattern;

public class Script {
    public static void main(String[] args) {
        FactoryMode fm = new FactoryMode(6.0f);
        CheckPoint checkPoint = new CheckPoint(8.7f,3.3f);
        fm.add_observer(checkPoint);
        fm.setPoint(6.0f);
        fm.setPoint(2.0f);
        fm.setPoint(9.0f);
    }
}