备忘录模式（Memento Pattern）

public class Memento {
    public String state;
    public Memento(String state){
        this.state = state;
    }
    public String getState() {
        return state;
    }
}

public class MementoManager {
    public List<Memento> list = new ArrayList<Memento>();
    public void add(Memento m) {
        list.add(m);
    }
    public Memento getMemento(int i) {
        return list.get(i);
    }
}

public class Adventor {
    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 m) {
        state = m.getState();
    }
}

public class Client {

    public static void main(String[] args) {
        Adventor adventor = new Adventor();
        adventor.setState("REST");
        
        MementoManager manager = new MementoManager();
        manager.add(adventor.saveStateToMemento());
        
        adventor.setState("BATTLE");
        
        manager.add(adventor.saveStateToMemento());
        
        System.out.println("Adventor current state " + adventor.getState());
        System.out.println("Adventor last state " + manager.getMemento(0).getState());
        adventor.getStateFromMemento(manager.getMemento(0));
        System.out.println("Adventor back to last state " + adventor.getState());

    }

}