Java Midpoint Rule (Rectangle Method)

Implementation of Midpoint Rule (Rectangle Method) (Integral Approximation) written in Java.

Enter beginning of interval: -2
Enter end of interval: 2
Enter number of iterations: 1000000
Integral is equal to: 5.333333333344218

import java.util.Scanner;

// ? 2018 TheFlyingKeyboard and released under MIT License
// theflyingkeyboard.net
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        double intervalBegin;
        double intervalEnd;
        int iterations;
        double integral = 0.0d;
        double step;

        System.out.print("Enter beginning of interval: ");
        intervalBegin = scanner.nextDouble();

        System.out.print("Enter end of interval: ");
        intervalEnd = scanner.nextDouble();

        System.out.print("Enter number of iterations: ");
        iterations = scanner.nextInt();

        step = (intervalEnd - intervalBegin) / iterations;

        for (int i = 1; i <= iterations; ++i) {
            integral += step * function(intervalBegin + (i - 1) * step);
        }

        System.out.println("Integral is equal to: " + integral);
    }

    private static double function(double x)
    {
        return x * x;
    }
}