备忘录模式（Memento）

1. 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。这样以后就可将该对象恢复到原先保存的状态。

2. 类图

   
   
   Memento

3. 例子

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());
    }
}

例子来源于这里
补充

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