Let’s learn java program to check whether number is prime or not.

## Java program to check whether number is prime or not

A prime number is a number that is greater than one and divided by itself. Prime numbers are those numbers which cannot be divided by other numbers than 1 or itself.

Also read – access modifiers in java

**Example :** 2, 3, 5, 7, 11, 13, 17….

In the below example for loop determines if given number is prime or not. In this for loop, condition is checked if number is divisible by any number in range number / 2.

We set “temp” to true and break out of for loop. Hence it is a prime number. If number is not divisible “temp” is false and number is prime number.

public class PrimeNumberInJava { public static void main(String[] args) { int a, b = 0, temp = 0; int number = 66; b = number / 2; if(number == 0 || number == 1) { System.out.println(number + " is not prime number"); } else { for(a = 2; a <= b; a++) { if(number % a == 0) { System.out.println(number + " is not prime number."); temp = 1; break; } } if(temp == 0) { System.out.println(number + " is prime number."); } } } }

**Output :**

Similarly let’s see java program using while loop,

import java.util.Scanner; public class JavaPrimeNumber { public static void main(String[] args) { boolean checkPrime = false; Scanner sc = new Scanner(System.in); System.out.println("Please enter any number : "); int number = sc.nextInt(); int a = 2; while(a <= number / 2) { if(number % a == 0) { checkPrime = true; break; } ++a; } if(checkPrime) { System.out.println(number + " is a prime number."); } else { System.out.println(number + " is not a prime number."); } sc.close(); } }

**Output:**

Please enter any number : 50

50 is not a prime number.

Now let’s see java program using method,

import java.util.Scanner; public class JavaPrimes { public static void main(String[] args) { Scanner sc = new Scanner(System.in); System.out.print("Please enter a number : "); int num = sc.nextInt(); if(checkPrime(num)) { System.out.println(num + " is a prime number."); } else { System.out.println(num + " is not a prime number."); } sc.close(); } public static boolean checkPrime(int number) { if(number <= 1) { return false; } for(int a = 2; a < Math.sqrt(number); a++) { if(number % a == 0) { return false; } } return true; } }

**Output:**

Please enter a number : 36

36 is not a prime number.

**NOTE:** 2 is the only even prime number. 0 and 1 are not prime numbers.