观察者模式在开源代码中的应用

梦里梦外; 2022-12-05 10:22 166阅读 0赞

观察者模式的作用：多个对象间存在一对多关系，当一个对象发生改变时，把这种改变通知给其他多个对象，从而影响其他对象的行为。

### **案例** ###

JDK 中对观察者模式的实现

观察者接口，实现该接口用于被通知发生变化，进行更新

public interface Observer {
        void update(Observable o, Object arg);
    }

Observable 相当于主题角色，可以注册、删除、通知观察者

public class Observable {
        private boolean changed = false;
        private Vector<Observer> obs;
        public Observable() {
            obs = new Vector<>();
        }
        public synchronized void addObserver(Observer o) {
            if (o == null)
                throw new NullPointerException();
            if (!obs.contains(o)) {
                obs.addElement(o);
            }
        }
        public synchronized void deleteObserver(Observer o) {
            obs.removeElement(o);
        }
        public void notifyObservers() {
            notifyObservers(null);
        }
        public void notifyObservers(Object arg) {
            Object[] arrLocal;
            synchronized (this) {
                if (!changed)
                    return;
                arrLocal = obs.toArray();
                clearChanged();
            }
            for (int i = arrLocal.length-1; i>=0; i--)
                ((Observer)arrLocal[i]).update(this, arg);
        }
        public synchronized void deleteObservers() {
            obs.removeAllElements();
        }
        protected synchronized void setChanged() {
            changed = true;
        }
        protected synchronized void clearChanged() {
            changed = false;
        }
        public synchronized boolean hasChanged() {
            return changed;
        }
        public synchronized int countObservers() {
            return obs.size();
        }
    }

--------------------

### 【Java学习资源】整理推荐 ###

*  [中介者模式的实际应用][Link 1]
 *  [观察者模式在开源代码中的应用][Link 2]
 *  [职责链模式在开源代码中的应用][Link 3]
 *  [命令模式在开源代码中的应用][Link 4]
 *  [策略模式在开源代码中应用][Link 5]
 *  [模板方法模式在开源代码中应用][Link 6]
 *  [组合模式在开源代码中的应用][Link 7]
 *  [享元模式在开源代码中的应用][Link 8]
 *  [外观模式在开源代码中的应用][Link 9]
 *  [装饰器模式在开源代码中的应用][Link 10]
 *  [桥接模式在开源代码中的应用][Link 11]
 *  [适配器模式在开源代码中的应用][Link 12]
 *  [代理模式在开源代码中的应用][Link 13]
 *  [原型模式在开源代码中的应用][Link 14]
 *  [建造者模式在开源代码中的应用][Link 15]
 *  [工厂模式在开源代码中的应用][Link 16]
 *  [单例模式在开源代码中的应用][Link 17]
 *  [编码规范][Link 18]
 *  [设计模式][Link 19]
 *  [重构][Link 20]
 *  [设计原则][Link 21]
 *  [面向对象到底是什么][Link 22]
 *  [代码质量有哪些评判标准？][Link 23]

--------------------

### 【Java面试题与答案】整理推荐 ###

*  [基础与语法][Link 24]
 *  [集合][Link 25]
 *  [网络编程][Link 26]
 *  [并发编程][Link 27]
 *  [Web][]
 *  [安全][Link 28]
 *  [设计模式][Link 29]
 *  [框架][Link 30]
 *  [算法与数据结构][Link 31]
 *  [异常][Link 32]
 *  [文件解析与生成][Link 33]
 *  [Linux][]
 *  [MySQL][]
 *  [Oracle][]
 *  [Redis][]
 *  [Dubbo][]

[Link 1]: https://www.javanav.com/val/4ed6da84a1734b9ebfc33fc0aa650f99.html
[Link 2]: https://www.javanav.com/val/187b108ea42d4992a1534e016c9ac618.html
[Link 3]: https://www.javanav.com/val/dc8fdb1954b1438ca55148e3c62547bd.html
[Link 4]: https://www.javanav.com/val/37ea584b5a9646f88e3916d13037e13f.html
[Link 5]: https://www.javanav.com/val/21eda51d16904f2798dc30974fe0fed9.html
[Link 6]: https://www.javanav.com/val/acd6815d8bcd45ce9db38659a049e778.html
[Link 7]: https://www.javanav.com/val/12f35b774b514c47a219bd860148f179.html
[Link 8]: https://www.javanav.com/val/72ac6d1ddd2d46b2a5312ac9b3050986.html
[Link 9]: https://www.javanav.com/val/f4a27593b46b46bc89d77d9f92c0f50c.html
[Link 10]: https://www.javanav.com/val/40716af16cda47ffae5fcf4090e69e14.html
[Link 11]: https://www.javanav.com/val/75bfae90731d40c781926a0dbec9edca.html
[Link 12]: https://www.javanav.com/val/f35536fdc771448f8d70574d830b7616.html
[Link 13]: https://www.javanav.com/val/24468130d26e460187c9280b90146649.html
[Link 14]: https://www.javanav.com/val/ffd6d3d1ceed414daafeb3ce10794c60.html
[Link 15]: https://www.javanav.com/val/e8afb788fdc54712aaf981c705796b46.html
[Link 16]: https://www.javanav.com/val/6f367ed6ee894adb830987f11536141c.html
[Link 17]: https://www.javanav.com/val/838b98837f574aa6a09c840921984707.html
[Link 18]: https://www.javanav.com/val/2b9f8790e8564bc0a2cb36357a66502f.html
[Link 19]: https://www.javanav.com/val/90b430ff0cbc4ef997e64cf7a0e1e745.html
[Link 20]: https://www.javanav.com/val/d9095cb3712040c0bee8054732321d6d.html
[Link 21]: https://www.javanav.com/val/9916617e210c4e0eae8649874a2cedd5.html
[Link 22]: https://www.javanav.com/val/5a834b46cfd945f7be9c4ea652306fd4.html
[Link 23]: https://www.javanav.com/val/0cea6c7c082043ab83ad87a9c5a48d9d.html
[Link 24]: https://www.javanav.com/interview/93b0069472fd479393006c0e73043fc4.html
[Link 25]: https://www.javanav.com/interview/4147d95e693945e7a50345fd33ec817e.html
[Link 26]: https://www.javanav.com/interview/68a57ffc78de4133bb890bdd502ac418.html
[Link 27]: https://www.javanav.com/interview/36a24fa3258e45c89873f474ce914912.html
[Web]: https://www.javanav.com/interview/4e27cb63adb440c6825a159d35cf4010.html
[Link 28]: https://www.javanav.com/interview/03affb2ce3f04fda8853f714e5764906.html
[Link 29]: https://www.javanav.com/interview/07a32a9ff17a4006a53550ce658cafed.html
[Link 30]: https://www.javanav.com/interview/5c466456e9b54ab0a749b5948e51f1d3.html
[Link 31]: https://www.javanav.com/interview/943f917041ee4f05add24539f5b861b2.html
[Link 32]: https://www.javanav.com/interview/d3f058cfc05d4c6dadd821b622e84d36.html
[Link 33]: https://www.javanav.com/interview/67a50996c28f418e83b109ea42fc3eff.html
[Linux]: https://www.javanav.com/interview/00cccb81729540d1923bd0a0ef49533a.html
[MySQL]: https://www.javanav.com/interview/d311e78502a845f1a4bb307bd6aec2b3.html
[Oracle]: https://www.javanav.com/interview/5f29e9677edf4a16be3dce30d257c9ab.html
[Redis]: https://www.javanav.com/interview/066c62b3af4d4827b2243a822c3084a9.html
[Dubbo]: https://www.javanav.com/interview/9a3e7a7740324757abaab953f7ebc455.html