class which method receives an Integer and returns an Integer that results of the square of each of the input Integer's digits. i.e. Input: 9119 Output: 811181

SquareDigit.java

import java.util.LinkedList;
import java.lang.Math;


public class SquareDigit {
  LinkedList<Integer> stack = new LinkedList<Integer>(); //stack where I'll push each digit for easy ordered extraction
  String str = "";
  
  /**
   * this method receives a number and returns a number which digits are the input number's digits square.
   * Ex: 9119 becomes 811181
   * @param int 
   * @return int
   */
  public int squareDigits(int n) {
    while (n > 0) {
      stack.push(n % 10);  //pushes remainder into stack (remainder is the last digit of the number)
      n = n / 10;
    }
    
    while (!stack.isEmpty()) { //cycle that extracts each of the digits from the stack, in LIFO order
      n = (int) stack.pop();
      str = str + (n * n); //String str becomes the concatenation of the popped digits, ie our objective
    }
    
    return Integer.valueOf(str); //converts the String obtained into an Integer and returns said number
  }
}