Java Program to find largest prime factor of a number

Following is the Java code to find the largest prime factor of a number −

Example

 Live Demo

import java.io.*; import java.util.*; public class Demo{    static long maxPrimeFactors( long val){       long max_prime = -1;       while (val % 2 == 0) {          max_prime = 2;          val >>= 1;       }       for (int i = 3; i <= Math.sqrt(val); i += 2){          while (val % i == 0){             max_prime = i;             val = val / i;          }       }       if (val > 2)       max_prime = val;       return max_prime;    }    public static void main(String[] args){       int val = 148592;       System.out.println("The largest prime factor of 148592 is ");       System.out.println(maxPrimeFactors(val));       val = 890654;       System.out.println("The largest prime factor of 890654 is ");       System.out.println(maxPrimeFactors(val));    } }

Output

The largest prime factor of 148592 is 251 The largest prime factor of 890654 is 4591

A class named Demo contains a static function that tales a value, and a ‘while’ condition is defined, which checks whether the value modulus 2 is 0. If it is 0, then, a variable (max_prime) is assigned the value 2. Otherwise, it is right bit shifted by 1. Again, a ‘for’ loop is iterated over elements from 3 to square root of the value, and incremented by 2 after every iteration.

Now, a ‘while’ loop checks if the value modulus iterator is 0. If yes, a variable (max_prime) is assigned the value that is currently being iterated. The value is divided by the iterated value. If this value is greater than 2, then this value (max_prime) is assigned to a variable named max_prime. This is returned. In the main function, an integer value is defined and the largest prime factor is found out by calling the function with the specific argument.