在不破坏封装性的前提下,捕获一个对象的内部状态,并在该状态之外保存这个状态。这样以后就可将该对象恢复到原先保存的状态。
public class Originator {
private String state; // 需要保存的属性
public String getState() {
return state;
}
public void setState(String state) {
this.state = state;
}
public Memento createMemento() { //创建备忘录,把自己的状态保存进去
return new Memento(state);
}
public void setMemento(Memento memento) { //根据备忘录恢复数据
state = memento.getState();
}
public void show() {
System.out.println("State is " + state);
}
}
//备忘录
public class Memento {
private String state;
public String getState() {
return state;
}
public Memento(String state) {
this.state = state;
}
}
//管理者
public class Caretaker {
private Memento memento;
public Memento getMemento() {
return memento;
}
public void setMemento(Memento memento) {
this.memento = memento;
}
}
// 客户代码
public static void main(String[] args) {
// TODO Auto-generated method stub
Originator originator = new Originator();
originator.setState("On");
originator.show();
Caretaker caretaker = new Caretaker();
caretaker.setMemento(originator.createMemento());
originator.setState("Off");
originator.show();
originator.setMemento(caretaker.getMemento());
originator.show();
}
//输出
State is On
State is Off
State is On
保存的细节封装在Memeto中,客户端并不需要持有Memeto对象。对象由需要保存状态的Originator创建,交给Caretaker保存。Originator恢复的时候也从Caretaker获取Memeto进行数据恢复。