- How to check, whether a number is prime number or not.
- Write a program in Java to check for prime numbers.

We have to check whether given **number is prime number or not**. First of all, we have to understand fundamentals of prime numbers.

- A
**Prime number**is a positive number greater than 1 that is only divisible by either 1 or itself. - All numbers other than prime numbers are known as composite numbers.
- Any non-prime number can be expressed as a factor of prime numbers.
- There are infinitely many prime numbers, here is the list of first few prime numbers

2 3 5 7 11 13 17 19 23 29 31 37....

## Java program to check for prime number

Let N be the number for primality testing. Here, we will use brute force approach by testing whether N is a multiple of any integer between 2 and N/2. This is the most basic method of checking the primality of a given integer N and is called trial division method.

package com.tcc.java.programs; import java.util.*; public class PrimeNumberCheck { public static void main(String args[]) { int num, i, isPrime = 0; Scanner in = new Scanner(System.in); System.out.println("Enter an Integer"); num = in.nextInt(); for(i = 2; i <= (num / 2); ++i) { if (num % i == 0) { isPrime = 1; break; } } // If isPrime is true then the num is prime otherwise non-prime if (isPrime == 0) System.out.println(num + " is a Prime Number"); else System.out.println(num + " is not a Prime Number"); } }Output

Enter an Integer 23 23 is a Prime Number

Enter an Integer 30 30 is not a Prime Number