Prime Number Program in Java

A Prime number is a number that is divisible only by 1 and itself. Example of prime numbers are 2, 3, 5, 7, 11, 13, 17???

Let's see an example program which gets an input from user and checks whether the given number is prime number or not.

Program

import java.io.*;
import java.util.*;

public class PrimeOrNot {
    public static void main(String[] args) {
        int number;
        boolean isPrime = true;
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter the number to check whether it is prime or not");
        number = scanner.nextInt();
        int midNumber = number / 2;

        if (number == 0 || number == 1) {
            System.out.println(number + " is not a prime number");
        } else {
            for (int i = 2; i <= midNumber; i++) {
                if (number % i == 0) {
                    isPrime = false;
                    break;
                }
            }
            if (isPrime) {
                System.out.println(number + " is a prime number");
            } else {
                System.out.println(number + " is not prime number");
            }
        }
    }
}

Output

Enter the number to check whether it is prime or not
17
17 is a prime number

Explanation

• Get the number as input from the user.
• If the number is 0 or 1 then its a prime number.
• If the number is greater than 1, start looping from 2 to the number/2 which is the mid number.
• Check whether the number is divisible by the looping number i, if its return 0 then its not a prime number.
• If the number is not divisible by any number in the loop then its a prime number.