等差数列の和を求める。

Main.java

public class Main {
    private static class ArithmeticProgression {
        private final int a, n, d;

        ArithmeticProgression(int a, int n, int d) {
            this.a = a;
            this.n = n;
            this.d = d;
        }

        private int calculateArithmeticSeries() {
            return n / 2 * (2 * a + (n - 1) * d);
        }
    }

    public static void main(String[] args) {
        ArithmeticProgression am = new ArithmeticProgression(1, 100, 1);
        int result = am.calculateArithmeticSeries();
        System.out.println(result);
    }
}