无涯教程-Java 备忘录模式备忘录模式(Memento)在不破坏封装性的前提下，捕获一个对象的内部状态，并在该对象之外

备忘录模式(Memento)在不破坏封装性的前提下，捕获一个对象的内部状态，并在该对象之外保存着这个状态。这样以后就可将该对象恢复到原先保存的状态，属于行为模式类别。

备忘录模式实例

记忆模式使用三个演员类，备忘录包含要还原的对象的状态，发起者在Memento对象中创建并存储状态，对象负责从Memento恢复对象状态。无涯教程创建了 Memento ， Originator 和 CareTaker 类。

演示类 MementoPatternDemo 将使用 CareTaker 和 Originator 对象显示对象状态的恢复。

第1步 - 创建Memento类。

Memento.java

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

第2步 - 创建Originator类

Originator.java

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();
}
}

第3步 - 创建CareTaker类

CareTaker.java

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);
}
}

第4步 - 使用 CareTaker 和 Originator 对象。

MementoPatternDemo.java

public class MementoPatternDemo {
   public static void main(String[] args) {
  </span><span class="typ">Originator</span><span class="pln"> originator </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Originator</span><span class="pun">();</span><span class="pln">
  </span><span class="typ">CareTaker</span><span class="pln"> careTaker </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">CareTaker</span><span class="pun">();</span><span class="pln">
  
  originator</span><span class="pun">.</span><span class="pln">setState</span><span class="pun">(</span><span class="str">"State #1"</span><span class="pun">);</span><span class="pln">
  originator</span><span class="pun">.</span><span class="pln">setState</span><span class="pun">(</span><span class="str">"State #2"</span><span class="pun">);</span><span class="pln">
  careTaker</span><span class="pun">.</span><span class="kwd">add</span><span class="pun">(</span><span class="pln">originator</span><span class="pun">.</span><span class="pln">saveStateToMemento</span><span class="pun">());</span><span class="pln">
  
  originator</span><span class="pun">.</span><span class="pln">setState</span><span class="pun">(</span><span class="str">"State #3"</span><span class="pun">);</span><span class="pln">
  careTaker</span><span class="pun">.</span><span class="kwd">add</span><span class="pun">(</span><span class="pln">originator</span><span class="pun">.</span><span class="pln">saveStateToMemento</span><span class="pun">());</span><span class="pln">
  
  originator</span><span class="pun">.</span><span class="pln">setState</span><span class="pun">(</span><span class="str">"State #4"</span><span class="pun">);</span><span class="pln">
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Current State: "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> originator</span><span class="pun">.</span><span class="pln">getState</span><span class="pun">());</span><span class="pln">		
  
  originator</span><span class="pun">.</span><span class="pln">getStateFromMemento</span><span class="pun">(</span><span class="pln">careTaker</span><span class="pun">.</span><span class="kwd">get</span><span class="pun">(</span><span class="lit">0</span><span class="pun">));</span><span class="pln">
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"First saved State: "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> originator</span><span class="pun">.</span><span class="pln">getState</span><span class="pun">());</span><span class="pln">
  originator</span><span class="pun">.</span><span class="pln">getStateFromMemento</span><span class="pun">(</span><span class="pln">careTaker</span><span class="pun">.</span><span class="kwd">get</span><span class="pun">(</span><span class="lit">1</span><span class="pun">));</span><span class="pln">
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Second saved State: "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> originator</span><span class="pun">.</span><span class="pln">getState</span><span class="pun">());</span><span class="pln">

}
}

第5步 - 验证输出。

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

无涯教程-Java 备忘录模式

备忘录模式实例

参考链接