设计模式学习—备忘录模式(Memento Design Pattern)

一、我的理解

备忘录模式用于存储某个类在某一时刻的状态。

二、实现方式

另外创建一个类Memento用于保存目标类的状态信息，然后由另一类来存储和管理这一系列保存的状态

三、实例

Java实例

Originator类：原始类，对该类的状态进行保存

package com.study.dp.memento;public class Originator {    private String state;    public String getState() {        return state;    }    public void setState(String state) {        this.state = state;    }        public Memento saveStateToMemento() {        return new Memento(state);    }        public void getStateFromMemento(Memento memento) {        this.state = memento.getState();    }    }

Memento类：备忘录类，保存目标类的状态信息

package com.study.dp.memento;public class Memento {    private String state;    public Memento(String state) {        super();        this.state = state;    }    public String getState() {        return state;    }    }

CareTaker类：备忘录管理类，存储和管理备忘录

package com.study.dp.memento;import java.util.ArrayList;import java.util.List;public class CareTaker {    private List<Memento> mementoList = new ArrayList<>();        public void add(Memento state) {        mementoList.add(state);    }        public Memento get(int index) {        return mementoList.get(index);    }    }

Demo类：测试

package com.study.dp.memento;public class Demo {    public static void main(String[] args) {        Originator originator = new Originator();        CareTaker careTaker = new CareTaker();        originator.setState("State #1");        originator.setState("State #2");        careTaker.add(originator.saveStateToMemento());        originator.setState("State #3");        careTaker.add(originator.saveStateToMemento());        originator.setState("State #4");                System.out.println("Current State: "+originator.getState());        originator.getStateFromMemento(careTaker.get(0));        System.out.println("First saved State: "+originator.getState());        originator.getStateFromMemento(careTaker.get(1));        System.out.println("Second saved State: "+originator.getState());    }    }

四、应用场景