备忘录模式

备忘录模式（Memento Pattern）保存一个对象的某个状态，以便在适当的时候恢复对象。

备忘录模式属于行为型模式。

实际案例

类信息概览：

类名 说明
Main.java 方法的总入口
Memento.java 记忆者
MementoManager.java 记忆管理者
Original.java 原始内容

定义

  • Memento.java
package com.ryo.design.pattern.note.memento;

/**
 * @author houbinbin
 * @version 1.0
 * @on 2017/8/17
 * @since 1.7
 */
public 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;
    }

}
  • MementoManager.java
package com.ryo.design.pattern.note.memento;

import java.util.LinkedList;
import java.util.List;

/**
 * @author houbinbin
 * @version 1.0
 * @on 2017/8/17
 * @since 1.7
 */
public class MementoManager {

    private List<Memento> mementoList = new LinkedList<>();

    public void add(Memento memento) {
        this.mementoList.add(memento);
    }

    public Memento get(int index) {
        return mementoList.get(index);
    }

}
  • Original.java
package com.ryo.design.pattern.note.memento;

/**
 * @author houbinbin
 * @version 1.0
 * @on 2017/8/17
 * @since 1.7
 */
public class Original {

    private String state;

    public String getState() {
        return state;
    }

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


    //-------------------public method;

    /**
     * 保存到 记忆体中
     * @return
     */
    public Memento saveToMemento() {
        return new Memento(this.getState());
    }

    /**
     * 从记忆体中获取对应的状态
     * @param memento
     */
    public void getStateFromMemento(Memento memento) {
        String state = memento.getState();
        this.state = state;;
    }

}

测试

  • Main.java
/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 * Copyright (c) 2012-2018. houbinbini Inc.
 * design-pattern All rights reserved.
 */

package com.ryo.design.pattern.note.memento;

/**
 * <p> </p>
 *
 * <pre> Created: 2018/5/23 下午8:46  </pre>
 * <pre> Project: design-pattern  </pre>
 *
 * @author houbinbin
 * @version 1.0
 * @since JDK 1.7
 */
public class Main {

    public static void main(String[] args) {
        Original original = new Original();
        MementoManager manager = new MementoManager();
        original.setState("State #1");
        original.setState("State #2");
        manager.add(original.saveToMemento());
        original.setState("State #3");
        manager.add(original.saveToMemento());
        original.setState("State #4");

        System.out.println("Current State: " + original.getState());
        original.getStateFromMemento(manager.get(0));
        System.out.println("First saved State: " + original.getState());
        original.getStateFromMemento(manager.get(1));
        System.out.println("Second saved State: " + original.getState());
    }

}
  • 测试结果
Current State: State #4
First saved State: State #2
Second saved State: State #3

实现方式

UML & Code

UML

UML 图示如下

Code

代码地址

备忘录模式

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