How To - Test for Prime Numbers

---

Description:

The below methods are the easiest and fastest ways to test for prime numbers.

Method 1: Simplest Way (in terms of Coding)

Here is the code for this method:

  public boolean isPrime(int n) {
      for (int i = 2; i <= n; i++) {
          if (n % i == 0) {
              return false; // n is not a prime number.
          }
      }
      return true; // n is a prime number.
  }

Method 2: Fastest Way (in terms of Processing)

Here is the code for this method:

  public boolean isPrime(long n) {
      // fast even test.
      if(n > 2 && (n & 1) == 0)
         return false;
      // only odd factors need to be tested up to n^0.5
      for(int i = 3; i * i <= n; i += 2)
          if (n % i == 0)
              return false;
      return true;
  }

---

---