设计模式学习—备忘录模式(Memento Design Pattern)

桃扇骨 2022-06-08 23:57 150阅读 0赞

# 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 #

![Center][]

###### 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 #

[Center]: /images/20220609/efd4b9d5c2914a7e92c7b164bfe033a8.png