In the previous article, we have discussed Java Program to Check Niven Number

In this article we are going to understand what Prime number is and how we can check whether a number is Prime or not in Java with examples.

## Java Program to Check Prime Number

**Prime numbers** are numbers which have no factors except one and itself.

Example: 19-> Prime number 678 -> Not a Prime number 99 -> Not a Prime number

In the above examples the number 19 is only a prime number.

Let’s see different ways to check prime number.

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**Approach:**

- We ask the user to enter a number which we store in an integer variable
`num`

. - We then use a while loop to iterate from 2 to the number itself and check if the number is divisible. If divisible then break out of the loop after setting
`flag`

=`false`

. - If
`flag`

is`true`

, it is said to be a Prime number or else it is not.

### Method-1: Java Program to Check Prime Number By Using Static Value

import java.util.Scanner; public class PrimeNumber { public static void main(String args[]) { //A number is declared int num = 7; //Iter is the iterator which starts from 2 as 1 divided every number int iter = 2; //Flag is used to record if the number is divisible after each iteration boolean flag = true; while (num > iter) { if (num % iter == 0) { flag = false; break; } iter++; } if (flag) { System.out.println(num+" is prime"); } else { System.out.println(num+" is not prime"); } } }

Output: 7 is prime

### Method-2: Java Program to Check Prime Number By Using User Input Value

import java.util.Scanner; public class PrimeNumber { public static void main(String args[]) { //Taking the number as input from the user using scanner class Scanner scan = new Scanner(System.in); System.out.print("Enter a number : "); int num = scan.nextInt(); //Iter is the iterator which starts from 2 as 1 divided every number int iter = 2; //Flag is used to record if the number is divisible after each iteration boolean flag = true; while (num > iter) { if (num % iter == 0) { flag = false; break; } iter++; } if (flag) { System.out.println(num+" is prime"); } else { System.out.println(num+" is not prime"); } } }

Output: Enter a number : 97 97 is prime

### Method-3: By C Language

#include <stdio.h> int main() { int num, i, flag = 0; printf("Enter a positive integer: "); scanf("%d", &num); for (i = 2; i <= num / 2; ++i) { //if it is divisible by any other number //thenit breaks if (num % i == 0) { flag = 1; break; } } if (num == 1) { printf("1 is unique number"); } else { if (flag == 0) printf("Prime number."); else printf("Not a prime number."); } return 0; }

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