林佳誼Java遞迴函數recursive function, 遞迴recursion

public class Main {//林佳誼w3schools遞迴函數recursion
  public static void main(String[] args) {
    int x =10;
    for (int i=0; i < x; i++){    //使用for迴圈
    System.out.print( i + "累加等於 " + sum(i) );
    System.out.println("累乘等於 " + f(i) ); }
  }
  public static int sum ( int k) {//定義sum函數,參數k
    if (k > 0) return k + sum(k - 1); //sum函數
    else return 0;  }
  public static int f ( int k) { //定義f函數,參數k
    if (k > 0) return k * f(k - 1); //f函數再呼叫f
    else return 1; } //0!=1, 5!=5x4x3x2x1
}