方法的递归调用

  public static void main(String[] args) {
        int n = 4;
        int revalue = sum(n);
        int add;
        System.out.println(revalue);  //15
    }
    public static int sum(int n ){
        if(n == 1){
        return 1;
        }
        int revalue = sum(n -1);
        int result = n+ revalue;
        return result;
    }