Simple Java Program to Check if a Number is Prime

Java Tutorial

Simple Java Program to Check if a Number is Prime

import Scanner class from util package.

import java.util.Scanner;

Source code:

import java.util.Scanner;

class CheckPrimeNum {

    static boolean checkPrime(int num) {

        boolean isPrime = true;

        for (int i = 2; i <= num / 2; i++) {

            if (num % i == 0) {

                isPrime = false;

            }

        }

        return isPrime;

    }

    public static void main(String args[]) {

        Scanner sc = new Scanner(System.in);

        System.out.println("Enter the Number");

        int num = sc.nextInt();

        checkPrime(num);

        if (checkPrime(num)) {

            if (num == 1) {

                System.out.println("Neither prime nor composite");

            } else {

                System.out.println("Prime Number");

            }

        } else {

            System.out.println("Composite Number");

        }

    }

}

Description:

• This Java program checks if a number is prime. A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers.

• The program uses a simple algorithm to check if a number is prime. The algorithm starts by checking if the number is 2. If the number is 2, then it is a prime number. Otherwise, the algorithm checks if the number is divisible by any number from 2 to the square root of the number. If the number is divisible by any of these numbers, then it is not a prime number. Otherwise, the number is a prime number. 

• The program is written in Java and can be run in any Java IDE.