Write a program to check the given number is a prime number or not?

Description:

A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself. A natural number greater than 1 that is not a prime number is called a composite number. For example, 5 is prime, as only 1 and 5 divide it, whereas 6 is composite, since it has the divisors 2 and 3 in addition to 1 and 6. The fundamental theorem of arithmetic establishes the central role of primes in number theory: any integer greater than 1 can be expressed as a product of primes that is unique up to ordering. This theorem requires excluding 1 as a prime.

Code:

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 package com.govindsblog.algos;   public class MyPrimeNumCheck {       public boolean isPrimeNumber(int number){                   for(int i=2; i<=number/2; i++){             if(number % i == 0){                 return false;             }         }         return true;     }           public static void main(String a[]){         MyPrimeNumCheck mpc = new MyPrimeNumCheck();         System.out.println("Is 17 prime number? "+mpc.isPrimeNumber(17));         System.out.println("Is 19 prime number? "+mpc.isPrimeNumber(19));         System.out.println("Is 15 prime number? "+mpc.isPrimeNumber(15));     } }

Output:

Is 17 prime number? true Is 19 prime number? true Is 15 prime number? false