设计模式之备忘录模式

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;
}

}

客户端代码：

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();

}
}

运行结果如下：

State=on

State=off

State=on