Implementing the Fibonacci sequence with recursion and adding memoization to improve the runtime

FibonacciSequence.java

public class FibonacciSequence {
  //using recursion without memoization
  public int calculateFibSequence(int n){
    //1st check for negative numbers and throw an exception
    if(n < 0){
      throw new IllegalArgumentException("No fibonacci sequence for negative numbers");
    } else if (n <=2){ //Base case 
      return n;
    } 
    //create a variable to store fib calculation result
    int result = calculateFibSequence(n-1) + calculateFibSequence(n-2);
    
    //return fib calculation result
    return result;
  }
}