Prime Number Program in Java

Here’s a simple program in Java to check if a number is prime or not:

import java.util.Scanner;

public class PrimeNumber {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int number = scanner.nextInt();
        scanner.close();
        
        boolean isPrime = true;
        
        // Check if the number is divisible by any number from 2 to half of the number
        for (int i = 2; i <= number / 2; 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.");
        }
    }
}

import java.util.Scanner;

public class PrimeNumber {

public static void main(String[] args) {

Scanner scanner = new Scanner(System.in);

System.out.print("Enter a number: ");

int number = scanner.nextInt();

scanner.close();

boolean isPrime = true;

// Check if the number is divisible by any number from 2 to half of the number

for (int i = 2; i <= number / 2; 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.");

}

Explanation:

The program asks the user to enter a number using the Scanner class.
The isPrime variable is initialized to true, assuming the number is prime.
The program checks if the number is divisible by any number from 2 to half of the number using a for loop.
If the number is divisible by any of these numbers, the isPrime variable is set to false, and the loop breaks.
After the loop ends, the program checks the value of isPrime and prints the appropriate message indicating whether the number is prime or not.

Here’s a version of the prime number program in Java 8 using lambda expressions and the IntStream API:

import java.util.Scanner;
import java.util.stream.IntStream;

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

        boolean isPrime = number > 1 && IntStream.range(2, (int) Math.sqrt(number) + 1)
                .noneMatch(i -> number % i == 0);

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