Java 觀察者模式( Observer Pattern)，observerpattern

Java 觀察者模式( Observer Pattern)，observerpattern
觀察者模式

在對象之間定義一對多的依賴，這樣一來，當一個對象改變狀態，依賴它的對象都會收到通知，並自動更新

package gx.subject;import gx.observer.Observer;/** * 主題介面 * @author always * */public interface Subject {    void registerObserver(Observer observer);    void removeObserver(Observer observer);    void notifyObserver();}

package gx.observer;/** *  * 接受到通知後 資料顯示的介面 *  * @author always * */public interface Display {    void display();}

package gx.observer;/** *  * 觀察者的介面 *  * @author always * */public interface Observer {    /**     * pull：觀察者自己獲得的想要的資料：“拉”     */    void update();    /**     * push：主題推送所有訊息給觀察者     *      * @param tiltle     * @param name     * @param summary     */    void update(String tiltle,String name,String summary);}

package gx.observer.impl;import gx.observer.Display;import gx.observer.Observer;import gx.subject.Subject;import gx.subject.impl.CurrentSubject;public class StudentObserver implements Observer,Display{    private Subject subject;    private String title;    private String name;    private String summary;    public StudentObserver(){    }    public StudentObserver(Subject subject){        this.subject=subject;        subject.registerObserver(this);    }    public void update() {        if (subject instanceof CurrentSubject) {            CurrentSubject cs = (CurrentSubject) subject;            this.name=cs.getName();            this.title=cs.getTitle();            this.display();        }    }    public void update(String title, String name, String summary) {        this.title=title;        this.name=name;        this.summary=summary;        this.display();    }    public void display() {        System.out.println("我是一名學生，今天我訂閱的新聞是：\n 新聞標題："+title+",新聞作者："+name+",新聞簡介:"+summary+";");    }}

package gx.observer.impl;import gx.observer.Display;import gx.observer.Observer;import gx.subject.Subject;import gx.subject.impl.CurrentSubject;public class TeacherObserver implements Observer,Display{    private Subject subject;    private String title;    private String name;    private String summary;    public TeacherObserver(){    }    public TeacherObserver(Subject subject){        this.subject=subject;        subject.registerObserver(this);    }    public void update() {        if (subject instanceof CurrentSubject) {            CurrentSubject cs = (CurrentSubject) subject;            this.name=cs.getName();            this.title=cs.getTitle();            this.display();        }    }    public void update(String title, String name, String summary) {        this.title=title;        this.name=name;        this.summary=summary;        this.display();    }    public void display() {        System.out.println("我是一名老師，今天我訂閱的新聞是：\n 新聞標題："+title+",新聞作者："+name+",新聞簡介:"+summary+";");    }}

package gx.subject.impl;import gx.observer.Observer;import gx.subject.Subject;import java.util.ArrayList;import java.util.List;/** * 這個例子：類比學生，老師 訂閱報紙 *  * 此對象改變 依賴它的對象：observerList 中的對象都會收到通知 *      setData-->notifyObserver-->observer.update()-->observer.display() * @author always * */public class CurrentSubject implements Subject {    private List<Observer> observerList;    private String title;    private String name;    private String summary;    public CurrentSubject(){        observerList=new ArrayList<Observer>();    }    public void registerObserver(Observer observer) {        if(observer!=null){            observerList.add(observer);        }    }    public void removeObserver(Observer observer) {        int indexOf = observerList.indexOf(observer);        if(indexOf!=-1){            observerList.remove(indexOf);        }    }    public void notifyObserver() {        for(Observer observer :observerList){            observer.update(title, name, summary);        }    }    public void setMessage(String title,String name,String summary){        this.title=title;        this.name=name;        this.summary=summary;        notifyObserver();    }    public String getTitle() {        return title;    }    public String getName() {        return name;    }    public String getSummary() {        return summary;    }}

測試類別

package gx.test;import junit.framework.TestCase;import gx.observer.Observer;import gx.observer.impl.StudentObserver;import gx.observer.impl.TeacherObserver;import gx.subject.impl.CurrentSubject;public class TestObserver extends TestCase{    public void testObserverPush(){        CurrentSubject cs= new CurrentSubject();        Observer observer=new StudentObserver(cs);        cs.registerObserver(new StudentObserver());        cs.registerObserver(new TeacherObserver());        cs.setMessage("設計模式","白","你好");//主題狀態改變：this.notifyObserver-->observer.update-->observer.display    }}