Java Program to find Given Number is Prime or Not

Let us see some of the conditions for a number to be prime:

1. A number is said to be a prime number if a number is divisible by 1 and only itself. A prime number has 2 divisors.

2. Negative numbers cannot be prime numbered.

3. '1' is not a prime number as it has only one positive divisor.

4. All even numbers are not prime, but '2' is an even prime number.

The following code does not check for negative numbers and it is for checking positive prime numbers.

/* Write a Java program to Find whether number is Prime or Not. */

class PrimeNumber
{
    public static void main(String args[])
    {
        int number = Integer.parseInt(args[0]);
        int flag=0;
        for(int i=2; i<number; i++)
    {
        if(number%i==0)
            {
                System.out.println(number+" is not a Prime Number");
                flag = 1;
                break;
            }
        }
        if(flag==0)
        System.out.println(number+" is a Prime Number");
    }
}

 OUTPUT:

Compile: javac PrimeNumber.java

Run Ex1: java PrimeNumber 11
11 is a Prime Number

Run Ex2: java PrimeNumber 15
15 is not a Prime Number