定义：在不破坏封装性的前提下中，捕获一个对象的内部状态，并在该对象之外保存这个状态。这样以后就可以将该对象恢复到原先保存的状态。

结构图：

示例代码：

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 String getState() {
		return state;
	}

	public void setState(String state) {
		this.state = state;
	}
	
	public void setState(Memento memento) {
		this.state = memento.getState();
	}
	
	public Memento createMemento() {
		
		return new Memento(state);
	}
	
	public void show() {
		System.out.println("State=" + state);
	}
}
public class Caretaker {

	private Memento memento;

	public Memento getMemento() {
		return memento;
	}

	public void setMemento(Memento memento) {
		this.memento = memento;
	}
	
}

public class Client {

	public static void main(String[] args) {
		
		Originator o = new Originator();
		o.setState("on");
		o.show();
		
		Caretaker c = new Caretaker();
		c.setMemento(o.createMemento());
		
		o.setState("off");
		o.show();
		
		o.setState(c.getMemento());
		o.show();
		
	}
}

State=on
State=off
State=on

设计模式之备忘录模式