备忘录模式

定义：在不破坏封装性的前提下，捕获一个对象的内部状态，并在该对象之外保存这个状态。这样就可以将该对象恢复到原先保存的状态

class Originator {  
    private String state = "";  
      
    public String getState() {  
        return state;  
    }  
    public void setState(String state) {  
        this.state = state;  
    }  
    public Memento createMemento(){  
        return new Memento(this.state);  
    }  
    public void restoreMemento(Memento memento){  
        this.setState(memento.getState());  
    }  
}  
  
class Memento {  
    private String state = "";  
    public Memento(String state){  
        this.state = state;  
    }  
    public String getState() {  
        return state;  
    }  
    public void setState(String state) {  
        this.state = state;  
    }  
}  
class Caretaker {  
    private Memento memento;  
    public Memento getMemento(){  
        return memento;  
    }  
    public void setMemento(Memento memento){  
        this.memento = memento;  
    }  
}  
public class Client {  
    public static void main(String[] args){  
        Originator originator = new Originator();  
        originator.setState("状态1");  
        System.out.println("初始状态:"+originator.getState());  
        Caretaker caretaker = new Caretaker();  
        caretaker.setMemento(originator.createMemento());  
        originator.setState("状态2");  
        System.out.println("改变后状态:"+originator.getState());  
        originator.restoreMemento(caretaker.getMemento());  
        System.out.println("恢复后状态:"+originator.getState());  
    }  
}