备忘录模式

Memento Pattern

将操作过程记录成便笺 Mementor ，使操作可以被记录，并随时可回退的设计模式

ref: 备忘录模式 | 菜鸟教程

public class Memento {
   private String state;
 
   public Memento(String state){
      this.state = state;
   }
 
   public String getState(){
      return state;
   }  
}

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

• 可以创建便笺

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

• 可储存便笺，并支持回退

public class MementoPatternDemo {
   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());
   }
}