Multiplying Large Numbers in JAVA without using BigInteger Class

I am practicing programs in java these days on the Website  http://www.javaladders.com. They have a 3-Stared problem called Multiplying Large Numbers. I found it pretty interesting.
The objective of this exercise is two multiply any 2 numbers. The numbers can be extremely large (i.e. run into hundreds of digits) and are provided as strings. 
You are not supposed to use the Java class Biginteger.
The expected output is a string which represents the product of the two numbers.
 In the following code I have used basic Java functions for doing operations on Strings.

Here is the code for the problem. You can enter any large numbers. 

Program:

  
import java.util.Scanner;
    public class LargeMultiply {
    // main method
    public static void main(String args[]) {
    System.out.println("\n\t \t WELCOME TO OneArmed Blog !!! \n");
    System.out.println("\t \t Multiplying 2 Large Numbers \n");
    Scanner sc = new Scanner(System.in);
    System.out.println("Enter 1st Number:"); //input first number
    String inputA = sc.next(); // taking string input
    System.out.println("Enter 2nd Number:"); //input second number
    String inputB = sc.next(); // taking string input
    LargeMultiply inst = new LargeMultiply();
                //Object creation of class LargeMultiply
    String v = inst.multiply(inputA, inputB); 
 // calling method multiply()
    System.out.println("RESULT:");
    System.out.println(v); // Output result
    }
    /*-- multiply method , return type String ,
 2 String parameters---- */
    public String multiply(String num1, String num2) {
    String[] str1 = num1.split("");
  //Split the number string into array with each element
 //   containing single digit
    String[] str2 = num2.split("");
    int m1 = 0;
    int m2 = 0;
    String[] resultStringArray = new String[str2.length];
    //Initializing the resultString array which has input 
 // string2 in Array form with each element
    //in different Index
    LargeMultiply inst1 = new LargeMultiply();
  //multiply every element of String2 with the String1
 //  using multiplySmall() method
    for (int j = str2.length - 1; j > 0; j--)
    resultStringArray[j] = inst1.multiplySmall(num1, str2[j]);
              // call to multiplySmall() method
    for (int i = num2.length() - 1; i > 0; i--) {
    for (int j = 1; j <= i; j++) {
    resultStringArray[j] = resultStringArray[j].concat("0");
 //concat number of zeroes which are equal to the number of
 //digits in 2nd number
    }
    }
    String finalResult = "0"; // Initialize output String
    for (int j = str2.length - 1; j > 0; j--) {
    finalResult = inst1.add(finalResult, resultStringArray[j]);
                      //call to adding large numbers method
    }
    return finalResult;  //return result
    }
 /*----Method to multiply a single digit to large digits----- */
    public String multiplySmall(String large, String small) {
    int smallInt = Integer.parseInt(small);
 //String to int conversion
    String[] s = large.split("");
    String[] largeStringArray = new String[s.length - 1];
                     //Initiate a String array
    //as discussed earlier split function makes
  //an array which has first element “” empty
    //so in order to remove that element 
 //we have to make another array,here it is
    //largeStringArray
    for (int i = 0; i < largeStringArray.length; i++) {
    largeStringArray[i] = s[i + 1];
    }
     
    int[] largeInt = new int[largeStringArray.length];
     //make a integer array for num1 which is considered large
    for (int i = 0; i < largeStringArray.length; i++) {
    largeInt[i] = Integer.parseInt(largeStringArray[i]);
      //String to int conversion of every element
    }
             //Logic for carry
    int carry = 0;
    String[] resultCarry = new String[2];
      //carry number represented by 2 element String array
    String result = "";// result to be stored in string form
    int resultInt = 0;//carry in form of integer
    //int count = 0;
    for (int i = largeStringArray.length - 1; i >= 0; i--) {
    resultInt = largeInt[i] * smallInt + carry;
 //multiplying every element of the largeInt
 //  with single digit integer
    carry = 0;//after every multiplication carry to be made zero
    if (i == 0) { // if no carry
    resultInt = resultInt;   // no change
    } else { // If carry then
    if (resultInt / 10 > 0) {
       //if output on multiplying is of 2 digits
    String s2 = Integer.toString(resultInt);
    //convert int to String
    String[] s3 = s2.split("");
 // Split the Result on basis of every digit
    carry = Integer.parseInt(s3[1]);
           //make the first digit stored on index 1, carry
    resultInt = resultInt % 10;
       //keep the unit place digit of the carry 
    //result which is concated later
    }
    }
    result = Integer.toString(resultInt).concat(result);
   //convert unit place of result to String and concat
 //   it with previous results
    }
    return result;
    //return result, which is multiplication of single
 // digit number of num2 to the whole num1
    }
   /*----------Method to add 2 large numbers-------- */
    public String add(String num1, String num2) {
    char[] tempChar1 = num1.toCharArray();
    //converting String num1 to character Array using
 //  toCharArray() function
    char[] tempChar2 = num2.toCharArray();
    //converting String num2 to character Array
  //using toCharArray() function
    char[] ch2;
    char[] ch1;
    //condition to check which number is longer
    if (tempChar1.length > tempChar2.length) { // if 1st is larger
    ch2 = tempChar1; // assign ch2 to num1
    ch1 = tempChar2; // assign ch1 to num2
    } else { //if second is larger
    ch2 = tempChar2;// assign ch2 to num2
    ch1 = tempChar1;// assign ch1 to num1
    } // so always the small number gets stored in ch1
    String ans = ""; //Initiating Result String, ans
    int tempAns = 0;
    int carry = 0;
    int smallerStringIndex;
    char smallerStringNumber;
    smallerStringIndex = ch1.length - 1;
    //represents index for smaller number
    for (int i = ch2.length - 1; i >= 0; i--) {
    //if index becomes negative add '0'
 // at the start of smaller digit, will have no effect
    if (smallerStringIndex < 0) {
    smallerStringNumber = '0';
    } else {
    smallerStringNumber = ch1[smallerStringIndex];
    }
    tempAns = (smallerStringNumber + ch2[i] - 96 + carry);
    // -96 the ASCII value gives actual value of the char in int
    if (tempAns >= 10) {
    //if there is a carry
    tempAns = tempAns - 10;
    //tempAns now contains the unit digit after addition
    ans = tempAns + ans;
    carry = 1; //assign 1 to carry
    } else {
    ans = tempAns + ans; //case of no carry
    carry = 0;
    }
    smallerStringIndex--; //reduce index by 1
    }
    if (carry == 1) {
    ans = "1" + ans;
    //adding String "1" to final result if at the 
 //end the last digits add up to give a carry
    }
    return ans; //return result in String
    }
    }

OUTPUT SCREEN :

Connect On G+ Shaurya Rohatgi