How To Check Whether a Number is a Harshad Number or Not in Java?

Java Server Side Programming Programming

Harshad number can be defined as a number which is divisible by the sum of its digits. Simply it means if the sum of the digits of the number is a factor of that number then it is a Harshad number.

In this article we will see how to check Harshad numbers by using the Java programming language.

To show you some instances

Instance-1

Input number is 18

Let’s check it by using the logic of Harshad number −

Sum of the digits of the number = 1 + 8 = 9.

So, 18 is divisible by 9.

Hence, 18 is a Harshad number.

Instance-2

Input number is 3

Let’s check it by using the logic of Harshad number −

Sum of the digits of the number = 3.

So, 3 is divisible by 3.

Hence, 3 is a Harshad number.

Instance-3

Input number is 15

Let’s check it by using the logic of Harshad number −

Sum of the digits of the number = 1 + 5 = 6.

So, 15 is not divisible by 6.

Hence, 14 is not a Harshad number.

Some other examples of Harshad numbers include 1, 2, 4, 5, 6, 7, 8, 9, 10, 12, 18, 20 etc.

Syntax

To convert integer value to String value by using inbuilt toString() method.

Following is the Syntax to get total number of digits in a number by converting the integer value to String value and then finding its length and assigning the length to an integer variable −

String str = Integer.toString(input_number);

To get the length of the Integer, we will use the Java String class inbuilt length() method which returns the length of the String object.

int length = st.length();

To get the character at a specific position/index in a string we use the charAt() method. Where charAt(i)-‘0’ returns the actual integer value.

int num = st.charAt(i)-‘0’;

Where ‘st’ refers to the string ‘i’ is the iterator variable to iterate the string.

Algorithm

Algorithm 1

Step 1 − Get an integer number either by initialization or by user input.
Step 2 − By iterating each digit of the number, find the sum of each digit of the number.
Step 3 − Then check if the original number is divisible by the sum of all digits of the number. If divisible then the given number is a Harshad number else it is not a Harshad number

Algorithm 2

Step 1 − Get an integer number either by initialization or by user input.
Step 2 − Convert that integer to String by using inbuilt toString() method.
Step 3 − Find the length of the String by using the inbuilt length() method.
Step 4 − Then by using a for loop, iterate till the length of the String and get one by one integer value from String by using charAt(i)-‘0’ and keep a track on the sum of all digits.
Step 5 − Then check if the original number is divisible by the sum of all digits of the number. If divisible then the given number is a Harshad number else it is not a Harshad number.

Multiple Approaches

We have provided the solution in different approaches

Without Using String
By Using String

Let’s see the program along with its output one by one.

Approach-1: Without Using String

In this approach, an integer value will be initialized in the program and then by using the Algorithm-1 we can check whether a number is a Harshad number or not.

Example


public class Main{
   //main method
   public static void main(String args[]){

      //Declared an integer variable and initialized a number as value
      int originalNumber = 21;

      //printing the given number to be checked
      System.out.println("Given number: "+originalNumber);

      //keep a copy of original number
      int copyOfOriginalNumber = originalNumber;

      //initialize sum as 0
      int sum = 0;

      //Find sum of all digits of the number
      //continue the loop till the number is greater than 0
      while(originalNumber > 0){

         //get the rightmost digit of the number by using % operator
         int rem = originalNumber%10;

         //add the digit(rem) to sum
         sum = sum + rem;

         //remove the rightmost digit from number and get the updated number
         originalNumber = originalNumber/10;
      }

      //printing the result
      if(copyOfOriginalNumber % sum == 0)
         System.out.println(copyOfOriginalNumber+" is a Harshadnumber");
      else
         System.out.println(copyOfOriginalNumber+" is not a Harshadnumber");
   }
}

Output

Given number: 21
21 is a Harshad number

Approach-2: By Using String

In this approach, an integer value will be initialized in the program and then by using the Algorithm-2 we will check if the number is a Harshad number or not.

Example


public class Main{
   //main method
   public static void main(String args[]){

      //Declared an integer variable and initialized a number as value
      int originalNumber = 40;

      //printing the given number to be checked
      System.out.println("Given number: "+originalNumber);

      //keep a copy of original number
      int copyOfOriginalNumber = originalNumber;

      //initialize sum as 0
      int sum = 0;

      //convert the integer to string by using toString() method
      String str = Integer.toString(originalNumber);
       
      //find length of String by using length() method
      //which is nothing but total number of digits in the given number
      int length=str.length();
       
      //iterate the String and get the digits by using charAt(i)-'0'
      //find the sum of digits
      for(int i = 0; i < length; i++){
         sum += str.charAt(i)-'0';
      }

      //printing the result 
      if(copyOfOriginalNumber % sum == 0)
         System.out.println(copyOfOriginalNumber+" is a Harshad number");
      else
         System.out.println(copyOfOriginalNumber+" is not a Harshad number");      
   }
}