Memento Pattern

Prepare a class that duplicates the state of a specific class and call it Memento. When user creates a duplicate, it instantiates Memento and records it in a collection, and retrieves the instance as needed.

Design Pattarm MENU

Check with the following class structure

class	Explanation
Origin.class	Class to be replicated
Memento.class	When duplicating Origin, duplicate Origin data in Memento and save Memento
MementoList.class	Holds a collection (List, Map, etc.) and stores a Memento instance
user(Main.class)	Check the operation

User Includes the meaning that other developers use this pattern

`Origin.class`


class Origin{
  int  No;

  void setNo(int No){
       this.No=No;
  }

  Memento createMemento(){
       return new Memento(No);
  }
}

`Memento.class`


class Memento{     
  int No;          //Have the same field as Origin

  Memento(int No){
      this.No=No;
  }

  int getNo(){
      return No;
  }
}

`MementoList.class`


class MementoList{
  Map  map = new HashMap();

  void put(int key,Memento mmt){
       map.put(key,mmt);
  }
  
  Memento getMemento(int key){
       return (Memento) map.get(key);
  }
}

`user(Main.class)`


public static void main(String[] args){
  Origin or = new Origin();
  MementoList list = new MementoList();

  or.setNo(1);
     list.put(1,or.createMemento());
  or.setNo(2);
     list.put(2,or.createMemento());

  Memento m1 = list.getMemento(1);
  System.out.println(m1.getNo());
}