java：递归算法

public class test {
  public static void main(String arg[]) {
    String s="abcde";
    char a[]=s.toCharArray();
    test t=new test();
    t.ni(a, a.length-1);
    System.out.println(t.jie(5));
    
    
  }
  //用递归做字符串反转，数组反转
  public void ni(char a[],int i){
    if(i>a.length||i<0) {
      return ;
    }else {
      System.out.print(a[i]);
      ni(a,i-1);
    }
  }
  //用递归做5！
  public int jie(int j) {
    if(j==0) {
      return 1;
    }
    return j*jie(j-1);
  }
  //用递归做1-100的和
  public int jia(int y) {
    if(y==0) {
      return 1;
    }
    return y+jia(y-1);
  }

}