Java Program to Check Whether a Number is Prime or Not

In this example, you will learn to check whether an entered number is a prime number or not.

A prime number is a whole number greater than 1 whose only factors are 1 and itself. A factor is a whole number that can be divided evenly into another number. The first few prime numbers are 2, 3, 5, 7, 11, 13, 17, 19, 23 and 29. Numbers that have more than two factors are called composite numbers.

public class Main {
    public static void main(String[] args) {

        int num = 29;
        boolean flag = false;
        for(int i = 2; i <= num/2; ++i)
        {
            // condition for nonprime number
            if(num % i == 0)
            {
                flag = true;
                break;
            }
        }

        if (!flag)
            System.out.println(num + " is a prime number.");
        else
            System.out.println(num + " is not a prime number.");
    }
}

public class Main {

public static void main(String[] args) {

int num = 29;

boolean flag = false;

for(int i = 2; i <= num/2; ++i)

{

// condition for nonprime number

if(num % i == 0)

{

flag = true;

break;

}

if (!flag)

System.out.println(num + " is a prime number.");

else

System.out.println(num + " is not a prime number.");

}

When you run above program, the output will be following:

29 is a prime number.

1	29 is a prime number.