观察者模式：

public class Observer {         private List<Target> targets;          public Observer() {             this.targets = new ArrayList<>();         }          public void register(Target target) {             this.targets.add(target);         }          //监听事件，在事件发生时做处理         public void observe() {             for (Target tar :targets) {                 System.out.println(tar); //do sth to observing targets              }         }     }      public class Target {      }      public class Subject {         public static void main(String[] args) {             Observer observer = new Observer();             for (int i = 0; i < 10; i++) {                 observer.register(new Target());             }             //发布事件             observer.observe();         }     }

单例模式：

public class Singleton {     public static getSingleton() {         return Inner.sg;     }      private static class Inner {         Singleton sg = new Singleton();     } }

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