Memento模式用于将对象的状态恢复到先前的状态. Memento模式属于行为模式类别.
Memento模式使用三个actor类. Memento包含要恢复的对象的状态. Originator在Memento对象中创建和存储状态,Caretaker对象负责从Memento恢复对象状态.我们创建了类 Memento , Originator 和 CareTaker .
MementoPatternDemo ,我们的演示类,将使用 CareTaker 和 Originator 对象来显示对象状态的恢复.
创建Memento类.
Memento.java
public class Memento { private String state; public Memento(String state){ this.state = state; } public String getState(){ return state; } }
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(); } }
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); } }
使用 CareTaker 和 Originator 对象.
MementoPatternDemo.java
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()); } }
验证输出.
Current State: State #4 First saved State: State #2 Second saved State: State #3