Memento Pattern

Memento.java

public class Memento {

	private String currentText;
	public Memento(String text){
		this.currentText = text;
	}
	
	public String getCurrentText(){
		return currentText;
	}
}

CareTaker.java

import java.util.ArrayList;

public class CareTaker {

	private ArrayListmementoList;
	
	public CareTaker(){
		mementoList = new ArrayList();
	}
	public void push(Memento memento){
		mementoList.add(memento);
	}
	public Memento pop(){
		Memento memento = mementoList.get(mementoList.size()-1);
		mementoList.remove(mementoList.size()-1);
		return memento;
	}
}

NotePad.java

public class NotePad {

	String currentText;
	private CareTaker careTaker;

	public NotePad(){
		careTaker = new CareTaker();
		currentText="";
	}
	public String getCurrentText() {
		return currentText;
	}
	public void setCurrentText(String currentText) {
		this.currentText = currentText;
	}
	public void appendString(String message){
		this.currentText+=message;
	}
	
	public Memento saveStateToMemento(){
		return new Memento(currentText);
	}
	
	public int hashCode() {
		return careTaker.hashCode();
	}
	public String toString() {
		return careTaker.toString();
	}
	public boolean equals(Object arg0) {
		return careTaker.equals(arg0);
	}
	
	public void save(){
		careTaker.push(new Memento(this.currentText));
	}
	public void undo(){
		Memento memento = careTaker.pop();
		this.currentText=memento.getCurrentText();
	}
}

MementoPatternDemo.java

import java.util.Scanner;

public class MementoPatternDemo {

	public static void main(String[] args) {
		//create the notepad class
		NotePad notepad = new NotePad();
		Scanner sc = new Scanner(System.in);
		
		//enter the string
		System.out.println("enter the string");
		notepad.appendString(sc.next());
		notepad.save();
		System.out.println("current Text saved ::"+notepad.getCurrentText());
		
		//enter next string
		System.out.println("enter the string");
		notepad.appendString(sc.next());
		notepad.save();
		System.out.println("current Text saved ::"+notepad.getCurrentText());
		
		//enter next string
		System.out.println("enter the string");
		notepad.appendString(sc.next());
		System.out.println("current Text saved ::"+notepad.getCurrentText());
				
		
		notepad.undo();
		System.out.println("after undo 1 current Text saved ::"+notepad.getCurrentText());
		notepad.undo();
		System.out.println("adter undo 2 current Text saved ::"+notepad.getCurrentText());
		
		
	}

}

Output