java实现前n项和，要求不使用循环、乘除法、判断标识

public class Ceui3 {

    public static int sum = 0;

    public static void main(String[] args) {
        System.out.println(sum(5));
    }

    private static int sum(int n){
        sum = sum + n;
        n --;
        try {
            byte[] a = new byte[n];
        }catch (Exception e){
            System.out.println("sum:" + sum);
            return sum;
        }
        return sum(n);
    }
}