public interface Observer { void update();}public class MotherObserver implements Observer { private String action; public String getAction() { return action; } public void setAction(String action) { this.action = action; } @Override public void update() { System.out.println(action); }public class FatherObserver implements Observer { private String action; public String getAction() { return action; } public void setAction(String action) { this.action = action; } @Override public void update() { System.out.println(action); }}import java.util.ArrayList;import java.util.List;public abstract class Subject { //關注者列表 List list = new ArrayList(); public void add(Observer observer) { list.add(observer); } public abstract void notifyObservers();}public class NotifySubject extends Subject { @Override public void notifyObservers() { for (Observer observer :list){ observer.update(); } }}public class MainTest { public static void main(String[] args) { System.out.println(“孩子哭了”); NotifySubject subject = new NotifySubject(); MotherObserver motherObserver = new MotherObserver(); motherObserver.setAction(“媽媽開始做飯”); FatherObserver fatherObserver = new FatherObserver(); fatherObserver.setAction(“爸爸開始準備玩具”); subject.add(motherObserver); subject.add(fatherObserver); subject.notifyObservers(); }}