观察者模式

观察者模式定义了对象之间的一对多依赖,这样依赖,当一个对象改变状态时,它的所有依赖者都会收到通知并自动更新

原则

• 为了交互对象之间的松耦合设计而努力,松耦合设计更有弹性更能应对变化

a.定义观察者模式

b.自己实现观察者模式

/** * Created by xjw on 2017/11/9 16:53 * Email 1521975316@qq.com */public class Test { public interface Display {  void display(); } public interface Observer {  void update(int a, int b, int c); } public interface Subject {  void addObserver(Observer observer);  void removeObserver(Observer observer);  void notifiObserver(); } static class WeekDate implements Subject {  private List<Observer> observers;  private int a;  private int b;  private int c;  public WeekDate() {   this.observers = new ArrayList<>();  }  @Override  public void addObserver(Observer observer) {   observers.add(observer);  }  @Override  public void removeObserver(Observer observer) {   int i = observers.indexOf(observer);   if (i >= 0) {    observers.remove(i);   }  }  @Override  public void notifiObserver() {   for (int i = 0; i < observers.size(); i++) {    observers.get(i).update(a, b, c);   }  }  public void setData(int a, int b, int c) {   this.a = a;   this.b = b;   this.c = c;   notifiObserver();  } } static class AObserver implements Observer, Display {  private int a;  private int b;  private int c;  public AObserver(Subject subject) {   subject.addObserver(this);  }  @Override  public void update(int a, int b, int c) {   this.a = a;   this.b = b;   this.c = c;   display();  }  @Override  public void display() {   System.out.println("a:" + a + ";b:" + b + ";c:" + c);  } } public static void main(String[] args) {  WeekDate subject = new WeekDate();  AObserver observer = new AObserver(subject);  subject.setData(1, 2, 3);  subject.setData(4, 5, 6);  subject.removeObserver(observer);  subject.setData(7, 8, 9); }}

c.Java提供的观察者模式

• 观察者接口(java.util.Observer)
• 可被观察者类(java.util.Observable),相当于主题Subject

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原标题：观察者模式

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