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.

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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());
}

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