Java 观察者模式

定义：定义了对象之间的一对多依赖，让多个观察者对象同时监听某一个主题对象，当主题对象发生变化时，它的依赖者（观察者）都会收到通知并更新

适用场景：

关联行为场景，建立一套触发机制

优点：

1.观察者和被观察者之间建立一个抽象的耦合

2.观察者模式支持广播通讯

缺点：

观察者之间有过多的细节依赖，提高时间消耗及程序复杂度

使用得当，要避免循环调用

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+"提交了问题");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;}@Overridepublic void update(Observable o,Object arg){Course course=(Course)o;Question question=(Question)arg;System.out.println(teacherName+"老师的"+course.getCourseName()+"课程接收到一个"+question.getUserName()+"提交的问答："+question.getQuestionContent());}
}

　　

public class Test {public static void main(String[] args) {Course course=new Course("Java设计模式精讲");Teacher teacher=new Teacher("laoshi");course.addObserver(teacher);Question question=new Question();question.setUserName("Geelly");question.setQuestionContent("Java");course.produceQuestion(course,question);}
}