Java Program to Check Perfect Number

Write a java program to check whether a number is perfect or not. Given an input number, we have to write a java code which check whether an input number is perfect number or not.

Before solving this problem, let's first understand what is a perfect number.

What is Perfect Number?

A perfect number is a positive integer that is equal to the sum of it's positive divisors  excluding the number itself.

For example -

6  is a perfect number. It's positive divisor is 1, 2 and 3 and sum of it's positive divisor is 6 (1 + 2 + 3).

Similarly, 28 is a perfect number. Sum of the positive divisor is 28 (1 + 2 + 4 + 7 + 14).

10 is not a perfect number. Sum of the positive divisor of 10 is 8 ( 1 + 2 + 5).

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Java Program to Check Perfect Number or Not

We have discussed what is a perfect number? Let's write a java code which takes an input number and check whether an input number is a perfect number or not.

package perfectnumber;

import java.util.*;

public class PerfectNumber {

    public static void main(String[] args) {

        int num, sum = 0;
        
        System.out.println("Enter a number");
            
        Scanner in = new Scanner(System.in);
        num = in.nextInt();
            
        /* If number is greater than zero */
        if (num > 0) {

          for (int i = 1; i < num; i++) {

            /* sum of it's factors */
            if ( num % i == 0) {
                sum = sum + i;
            }
        }
    
          if ( sum == num) {
              System.out.println(num + " is a perfect number ");

          } else {
              System.out.println (num + " is not a perfect number ");
          }
            
       }   else {
                
            System.out.println (" Please enter positive number ");
       }
   }
    
}

Output : 

Enter a number  :    28

28 is a perfect number

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