Java 觀察者模式

定義：定義了對象之間的一對多依賴，讓多個觀察者對象同時監聽某一個主題對象，當主題對象發生變化時，它的依賴者（觀察者）都會收到通知並更新

適用場景：

關聯行為場景，建立一套觸發機制

優點：

1.觀察者和被觀察者之間建立一個抽象的耦合

2.觀察者模式支持廣播通訊

缺點：

觀察者之間有過多的細節依賴，提高時間消耗及程序復雜度

使用得當，要避免循環調用

import java.util.Observable;

public class Course extends Observable {
    private  String courseName;

    public Course(String courseName) {
        this.courseName = courseName;
    }

    public String getCourseName() {
        return courseName;
    }
    public void produceQuestion(Course course,Question question){
        System.out.println(question.getUserName()+"在"+course.courseName+"提交了問題");
        setChanged();
        notifyObservers(question);
    }
}

　　

public class Question {
    private String userName;
    private String questionContent;

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getQuestionContent() {
        return questionContent;
    }

    public void setQuestionContent(String questionContent) {
        this.questionContent = questionContent;
    }
}

　　

import java.util.Observable;
import java.util.Observer;


public class Teacher implements Observer {
    private String teacherName;

    public Teacher(String teacherName) {
        this.teacherName = teacherName;
    }
    @Override
    public void update(Observable o,Object arg){
       Course course=(Course)o;
       Question question=(Question)arg;
        System.out.println(teacherName+"老師的"+course.getCourseName()+"課程接收到一個"+question.getUserName()+"提交的問答："+question.getQuestionContent());

    }
}

　　

public class Test {
    public static void main(String[] args) {
        Course course=new Course("Java設計模式精講");
        Teacher teacher=new Teacher("laoshi");
        course.addObserver(teacher);

        Question question=new Question();
        question.setUserName("Geelly");
        question.setQuestionContent("Java");

        course.produceQuestion(course,question);
    }
}