Check for Prime Number in Java

The following code shows how to Check for Prime Number in Java. Prime numbers are those numbers which are divisible only by 1 or itself.

The following code determines whether a randomly generated number is a prime number or not. The function Math.random() generates a random number in the range 0 to 1. In order to find the number in the range 0 to 100, we need to multiply the number returned by Math.random() by 100. Hence, we get a number between 0 and 100. Further, we can start a loop and check whether the given number is divisible by any other number between 2 and half of the given number. In case, it is divisible the number is not prime. Otherwise, the number is prime.

public class Main
{
	public static void main(String[] args) {
		int a_number, min=0, max=100;
		System.out.println("Randomly generating a number in the range ["+min+", "+max+"]: ");
		a_number=(int)(Math.random()*100);
		System.out.println(a_number);
		boolean prime=true;
		for(int i=2;i<=a_number/2;i++)
		{
		    if(a_number%i==0)
		    {
		        prime=false;
		        break;
		    }
		}
		if(prime)
		{
		    System.out.println(a_number+" is prime!");
		}
		else{
		    System.out.println(a_number+" is not prime!");
		}
	}
}

Output

Randomly generating a number in the range [0, 100]:
96
96 is not prime!

Randomly generating a number in the range [0, 100]:
69
69 is not prime!

Randomly generating a number in the range [0, 100]:
53
53 is prime!

Further Reading