Java设计模式之java备忘录模式详解

public class Originator {
    private String state;//状态
    public String getState() {
        return state;
    }
    public void setState(String state) {
        this.state = state;
    }
    //编写一个方法，可以保存一个状态对象Memento
    public Memento saveStateMemento(){
        return new Memento(state);
    }
    public void getStateFromMemento (Memento memento){
        state = memento.getState();
    }
}

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

public class Caretaker {
    //List集合中会有很多备忘录对象
    private List<Memento> mementoList = new ArrayList<>();
    public void add(Memento memento) {
        mementoList.add(memento);
    }
    //获取到第index个Origintor的备忘录对象
    public Memento get(int index){
        return mementoList.get(index);
    }
}

//原发器，需要保存对象的状态
@Data
@AllArgsConstructor
public class Chessman
{
    private String label;//当前棋子的名字: 车，炮，马
    private Integer x,y;//当前棋子的坐标
    //保存当前对象的状态--备份数据
    public ChessmanMemento save()
    {
        return new ChessmanMemento(label,x,y);
    }
    //恢复当前对象的状态
    public void restore(ChessmanMemento chessmanMemento)
    {
        this.label=chessmanMemento.getLabel();
        this.x=chessmanMemento.getX();
        this.y=chessmanMemento.getY();
    }
    //展示当前对象的状态
    public void show()
    {
        System.out.println(
                String.format("棋子: %s ,位置: [%d,%d]",label,x,y)
        );
    }
}

//负责备份的棋子状态
@Data
@AllArgsConstructor
public class ChessmanMemento
{
    private String label;
    private Integer x,y;
}

//负责保存多个备份对象
public class MementoCaretaker
{
   //记录当前所处的备份状态
   Integer index=-1;//一开始没有备份数据
  //通过一个List集合保存多个备份对象
    List<ChessmanMemento> chessmanMementoLinkedList= Lists.newLinkedList();
  //悔棋操作--恢复到上一个备忘录状态
    public  ChessmanMemento getMemento()
    {
        if(index<=0)
        {
            throw new IndexOutOfBoundsException("已经无棋可悔了");
        }
        this.index--;//当前所处的备份状态减去一
        //将当前状态之后的状态全部清空
        //保留前index个元素，并将流收集到List中
        chessmanMementoLinkedList = chessmanMementoLinkedList.stream()
                .limit(this.index+1).collect(Collectors.toList());
        return chessmanMementoLinkedList.get(index);
    }
    //下棋---增加新的备份对象
    public void addMemento(ChessmanMemento chessmanMemento)
    {
        index++;
        chessmanMementoLinkedList.add(chessmanMemento);
    }
}

//客户端
public class Client
{
  //维护一个守护者对象
  MementoCaretaker mementoCaretaker=new MementoCaretaker();
 //下棋
    public void play(Chessman chessman)
    {
        //通过调用备份返回，返回一个备份对象，添加进备份集合中去
        mementoCaretaker.addMemento(chessman.save());
    }
 //悔棋
    public void undo(Chessman chessman)
    {
        //得到上一次记录的备份状态对象
        ChessmanMemento memento = mementoCaretaker.getMemento();
        //调用恢复功能
        chessman.restore(memento);
    }
}

public class Test
{
    public static void main(String[] args) {
        //创建棋子对象
        Chessman chessman=new Chessman("车",1,1);
        //创建一个客户端
        Client client=new Client();
        client.play(chessman);
        chessman.show();
        chessman=new Chessman("马",2,0);
        client.play(chessman);
        chessman.show();
        //悔棋
        client.undo(chessman);
        chessman.show();
        client.undo(chessman);
        chessman.show();
    }
}