How to check whether a number is a perfect number or not in java?

The Perfect Number is a special type of positive number. When the number is equal to the sum of its positive divisors excluding the number, it is called a Perfect Number.

For example, 28 is the perfect number because when we sum the divisors of 28, it will result in the same number. The divisors of 28 are 1, 2, 4, 7, and 14. 28 = 1 + 2 + 4 + 7 + 14
28 = 28

Let’s see the logic to check it,

Solution

package com.javacodepoint.programs;

public class CheckPerfectNumber {
    
    public static void main (String[] args){   
        
    	System.out.println("All Perfect numbers between 1 - 1000:");   
    	
        for (int i = 1; i < 1000; i++ ){   
            if (isPerfectNumber(i)) {
            	System.out.println( i +" is a perfect number");
            }   
        }  
    } 
    
    
    /*
     * Method that will return true when number will be perfect   
     */
    static boolean isPerfectNumber(int number) {   
        
    	int sum = 1;   
    
        // Finding all the divisors   
        for (int i = 2; i * i <= number; i++) {   
            if (number % i == 0) {   
                if(i * i != number) {   
                    sum = sum + i + number / i;   
                } else { 
                    sum = sum + i;  
                }
            }   
        }    
        
        // Checking whether the sum of all divisors and number both are equal or not  
        if (sum == number &amp;&amp; number != 1) {  
            return true;   
        }
        
        return false;   
    }
}

OUTPUT:

All Perfect numbers between 1 – 1000:
6 is a perfect number
28 is a perfect number
496 is a perfect number