递归方法求前n项和

public class Demo01Recurison {
    public static void main(String[] args) {
        int sums = sum(3);
        System.out.println(sums);

    }

    private static int  sum(int n) {
    if(n==1){
        return 1;
    }
    return n+sum(n-1);
    }
}