新入门菜鸟，老师讲课的时候睡着了，求大神可以逐条讲解一下<(*￣▽￣*)/<(*￣▽￣*)/

class DengCha {
    int start, d;
    DengCha() {    }
    DengCha(int start, int d) {
        this.start = start;
        this.d = d;
    }
    void setStart(int s) {
        start = s;
    }
    void setD(int d) {
        this.d = d;
    }
    int getSum(int n) {
        int sum = 0, i = 1;
        while (i <= n) {
            sum = sum + start;
            start = start + d;
            i++;
        }
        return sum;
    }
}

public class ZuoYe2_1 {
    public static void main(String args[]) {
        DengCha shulie = new DengCha(2, 3);
        System.out.println(shulie.getSum(100));
        shulie.setStart(10);
        shulie.setD(5);
        System.out.println(shulie.getSum(9));
    }
}