备忘录模式
备忘录模式(Memento Pattern)用来恢复一个对象的状态到以前的状态
实现
这个示例中,备忘录模式(Memento Pattern)使用三个操作者类。 Memento类中包含要恢复的对象的状态。 创建者在Memento对象中创建和存储状态,Caretaker对象负责从Memento中恢复对象状态。在这个示例中,创建了以下几个类:Memento,Originator和CareTaker,将使用CareTaker和Originator对象来显示对象状态的恢复。
代码
package com.test;
import java.util.ArrayList;
import java.util.List;
//第1步,创建一个Memento类
class Memento {
private String state;
public Memento(String state) {
this.state = state;
}
public String getState() {
return state;
}
}
// 第2步, 创建一个Originator类
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,创建一个CareTaker类
class CareTaker {
private List mementoList = new ArrayList();
public void add(Memento state) {
mementoList.add(state);
}
public Memento get(int index) {
return mementoList.get(index);
}
}
public class Test {
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());
}
}
运行结果:
Current State: State #4
First saved State: State #2
Second saved State: State #3