Prime Number Program in Java: Simple Logic

The Prime Number Program in Java is a simple yet essential program that determines whether a given number is prime or not.

What is a Prime Number ?

A prime number is a positive number greater than 1 which is only divisible by 1 and the number itself.

Some examples of prime numbers are : 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47

Steps for Prime Number Program in Java

We will follow the below steps to writing the Prime Number program in Java.

• In this program, the user is prompted to enter a number.
• It iterates from 2 to the square root of the number and checks if any number divides the entered number evenly.
• If a divisor is found, the number is not prime. Otherwise, it is considered prime.

Using For Loop

Java Code Snippet

import java.util.Scanner;

public class PrimeNumberProgram {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a number: ");

        while (!scanner.hasNextInt()) {
            System.out.println("Invalid input. Please enter a valid positive integer: ");
            scanner.next();
        }

        int number = scanner.nextInt();
        scanner.close();

        if (number <= 1) {
            System.out.println("The entered number is not a valid candidate for a prime number.");
        } else {
            boolean isPrime = true;

            for (int i = 2; i <= Math.sqrt(number); 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 a prime number.");
            }
        }
    }
}

Enter a number: 10
10 is not a prime number.

Using While Loop

Java Code Snippet

import java.util.Scanner;

public class PrimeNumberProgram {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a number: ");

        while (!scanner.hasNextInt()) {
            System.out.println("Invalid input. Please enter a valid positive integer: ");
            scanner.next();
        }

        int number = scanner.nextInt();
        scanner.close();

        if (number <= 1) {
            System.out.println("The entered number is not a valid candidate for a prime number.");
        } else {
            boolean isPrime = true;
            int i = 2;

            while (i <= Math.sqrt(number)) {
                if (number % i == 0) {
                    isPrime = false;
                    break;
                }
                i++;
            }

            if (isPrime) {
                System.out.println(number + " is a prime number.");
            } else {
                System.out.println(number + " is not a prime number.");
            }
        }
    }
}

Output

Enter a number: 11
11 is a prime number.

Conclusion

The Prime Number Program in Java allows users to input a number and determine if it is a prime number or not.

Related Article

Simple Java Programs asked in Interviews