备忘录模式也是行为模式的一种，主要是提供一种保存内部状态的方法，方便在合适的时候恢复。简单实现：
备忘录实体类：
public class Memento {
private String state;
public Memento(String state){
this.state = state;
}
public String getState(){
return state;
}
}
备忘录的应用类
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();
}
}
备忘录管理类
public class MementoManager {
private ArrayList<Memento> mementoList = new ArrayList<>();
public void add(Memento state){
mementoList.add(state);
}
public Memento get(int index){
return mementoList.get(index);
}
}
测试类
public static void main(String[] args) {
Originator originator = new Originator();
MementoManager manager = new MementoManager();
originator.setState("state 1");
originator.setState("state 2");
manager.add(originator.saveStateToMemento());
originator.setState("state 3");
manager.add(originator.saveStateToMemento());
originator.setState("state 4");
System.out.println(originator.getState());
System.out.println(manager.get(0).getState());
}
