19) Memento pattern

类别：

 Behavioral Pattern (备忘录模式）

问题：

 

方案：

 

 

示例：

 

import java.util.ArrayList;
import java.util.List;

public class MementoPatternDemo {
    public static void main(String[] args) {
        Scene scene = new Scene();
        List<Memento> mementoList = new ArrayList<Memento>();
        scene.setState("State #1");
        scene.setState("State #2");
        mementoList.add(scene.snapshootToMemento());
        scene.setState("State #3");
        mementoList.add(scene.snapshootToMemento());
        scene.setState("State #4");
        System.out.println("Current State: " + scene.getState());
        scene.recoverFromMemento(mementoList.get(0));
        System.out.println("First saved State: " + scene.getState());
        scene.recoverFromMemento(mementoList.get(1));
        System.out.println("Second saved State: " + scene.getState());
    }

}

class Memento {
    private String state;

    public Memento(String state) {
        this.state = state;
    }

    public String getState() {
        return state;
    }
}

class Scene {
    private String state;

    public void setState(String state) {
        this.state = state;
    }

    public String getState() {
        return state;
    }

    public Memento snapshootToMemento() {
        return new Memento(state);
    }

    public void recoverFromMemento(Memento Memento) {
        state = Memento.getState();
    }
}

 

Current State: State #4
First saved State: State #2
Second saved State: State #3

 

应用：

 

不足：(

 

优化：）