Digit sum loops+random positive number generator

Question

I have to prepare program that summing the digits of two given by user numbers and then give back the random number which is

• natural number
• the digit sum of this number is bigger then the digit sum of given by user numbers

It's look like everything is ok but i dont know if it is just luck in random number generator or it's working well. Thank you for review.

import java.util.Random;


import java.util.Scanner;


public class Ex1 {

public static void main(String[] args) {
    Random rnd = new Random();
    Scanner scn = new Scanner(System.in);
    int sum1 = 0;
    int sum2 = 0;
    int sum3 = 0;
    int sum4 = 0;
    System.out.println("1TH NUMBER : ");
    int a1 = scn.nextInt();
    System.out.println("2ND NUMBER : ");
    int a2 = scn.nextInt();
    System.out.println((0 > a1 || 0 > a2 ? "ERROR-NEGATIVE NUMBER" : "OK"));
    while (a1 > 0) {
        sum1 += a1 % 10;
        a1 /= 10;
    }
    //System.out.println(sum1);
    while (a2 > 0) {
        sum2 += a2 % 10;
        a2 /= 10;
    }
    //System.out.println(sum2);
    int temp = sum1 + sum2; //temporary-for storage /=
    while (temp > 0) {
        sum3 += (temp) % 10;
        (temp) /= 10;
    }
    // System.out.println(sum3);
    while (true) {
        int a3 = rnd.nextInt(Integer.MAX_VALUE);
        sum4 += (a3) % 10;
        (a3) /= 10;
       // System.out.println(sum4);
        if (sum4 > sum3) {
            System.out.println(a3 + " this is my number");
            break;
        }
    }

}
}

Answer 1

I have some suggestion for you.

Code duplication

In your code, you have some code duplication that can be extracted in a method. By extracting the code, the code will become shorter, be less error-prone and easier to read.

1. I suggest that you make a method to print a question and read the user input.

public static void main(String[] args) {
   //[...]
   int a1 = askQuestionAndReceiveAnswer(scn, "1TH NUMBER : ");
   int a2 = askQuestionAndReceiveAnswer(scn, "2ND NUMBER : ");
   //[...]
}


private static int askQuestionAndReceiveAnswer(Scanner scn, String s) {
   System.out.println(s);
   return scn.nextInt();
}

2. Since the logic is the same to handle the sum, you can extract both of the while into a method. This extraction will remove lots of code!

public static void main(String[] args) {
   //[...]
   int sum1 = getSum(a1);
   int sum2 = getSum(a2);

   int temp = sum1 + sum2; //temporary-for storage /=

   int sum3 = getSum(temp);
   //[...]
}

private static int getSum(int userInput) {
   int currentSum = 0;
   while (userInput > 0) {
      currentSum += userInput % 10;
      userInput /= 10;
   }
   return currentSum;
}

Other observations

1. In my opinion, I would extract the last calculation in a method and return the result.

public static void main(String[] args) {
   //[...]
   int number = findNumber(rnd, sum3);
   System.out.println(number + " this is my number");
   //[...]
}

private static int findNumber(Random rnd, int sum3) {
   int sum4 = 0;
   while (true) {
      int a3 = rnd.nextInt(Integer.MAX_VALUE);
      sum4 += (a3) % 10;
      (a3) /= 10;
      if (sum4 > sum3) {
         return a3;
      }
   }
}

Refactored code

public static void main(String[] args) {
   Random rnd = new Random();
   Scanner scn = new Scanner(System.in);

   int a1 = askQuestionAndReceiveAnswer(scn, "1TH NUMBER : ");
   int a2 = askQuestionAndReceiveAnswer(scn, "2ND NUMBER : ");
   System.out.println((0 > a1 || 0 > a2 ? "ERROR-NEGATIVE NUMBER" : "OK"));

   int sum1 = getSum(a1);
   int sum2 = getSum(a2);
   int temp = sum1 + sum2; //temporary-for storage /=

   int sum3 = getSum(temp);

   int number = findNumber(rnd, sum3);
   System.out.println(number + " this is my number");
}

private static int findNumber(Random rnd, int sum3) {
   int sum4 = 0;
   while (true) {
      int a3 = rnd.nextInt(Integer.MAX_VALUE);
      sum4 += (a3) % 10;
      (a3) /= 10;
      if (sum4 > sum3) {
         return a3;
      }
   }
}

private static int getSum(int userInput) {
   int currentSum = 0;
   while (userInput > 0) {
      currentSum += userInput % 10;
      userInput /= 10;
   }
   return currentSum;
}

private static int askQuestionAndReceiveAnswer(Scanner scn, String s) {
   System.out.println(s);
   return scn.nextInt();
}

Answer 2

Welcome to Code Review, you are not closing the Scanner resource and this is a resource leak: to avoid this you can use from java 8 the construct try-with-resource like below:

try (Scanner scn = new Scanner(System.in)) {
    //here your code
}

You can write your line:

System.out.println((0 > a1 || 0 > a2 ? "ERROR-NEGATIVE NUMBER" : "OK"));

using Math.min in the following way:

System.out.println(Math.min(a1, a2) < 0 ? "ERROR-NEGATIVE NUMBER" : "OK");