Undo Redo Program in Java using Data Structures

Welcome back again!

In this post we will learn that how actually we can undo and redo LinkedList in java programRequirements:

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agenda:
           Node
                 +data:String
                  +next:Node
           LinkedList
                 +head: Node
                 +insertAtEnd(Node data):void
                 +undo():Node
                 +redo():void
           LinkedList Runner
                   main()

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Code for Node class public class Node { public String data; public Node next; public Node(String data) { this.data = data; this.next = null; } }                                           Code for LinkedList class public class LinkedList  {  public Node head;  public String str = "";  public LinkedList() {  head = null;  }  public void insertAtEnd(Node node)  {  if(isEmpty()) head = node;  else { Node curr = head;  while(curr.next!=null)  {  curr = curr.next;  }  curr.next = node;  }  }  public void redo() {  if(str.equals("")) return;  else  {  insertAtEnd(new Node(str.charAt(str.length()-1)+""));  str = str.replaceAll(str.charAt(str.length()-1)+"", "");  }  }  public Node undo() {  if(isEmpty()) return null;  else  {  Node curr = head; while(curr.next.next != null) {  curr = curr.next;  }  Node temp = curr.next; str+=temp.data; curr.next = null; return temp;  }  }  public boolean isEmpty() {  return head == null;  }  public void showAll() {  if(isEmpty()) System.out.println("LinkedList is empty");  else  {  Node curr = head; while(curr!=null)  {  System.out.println(curr.data); curr = curr.next;  }  }  }end methods  }end class Code for Runner class public class LinkedListRunner { public static void main(String[] args) { LinkedList list = new LinkedList(); list.insertAtEnd(new Node("A")); list.insertAtEnd(new Node("B")); list.insertAtEnd(new Node("C")); list.insertAtEnd(new Node("D")); list.insertAtEnd(new Node("E")); list.showAll(); System.out.println("_____undo_________"); Node result = list.undo(); Node result2 = list.undo(); Node result3 = list.undo(); // System.out.println(result.data); // System.out.println(result2.data); // System.out.println(result3.data); list.showAll(); System.out.println("____________after redo__________"); list.redo(); list.redo(); // System.out.println(list.str); list.showAll(); } }

By M Fahad Shahzad(Blogger)