406 遞迴字串計算

import java.util.Scanner;
public class JPA406 {
    static Scanner keyboard = new Scanner(System.in);
    public static void main(String args[]) {
String s;

      System.out.print("Input a string: ");
      s=keyboard.nextLine();
      System.out.println(s+" has "+countA(s)+" As");
      System.out.print("Input a string: ");
      s=keyboard.nextLine();
      System.out.println(s+" has "+countA(s)+" As");

    }

    public static int countA(String str) {
if(str.equals("")){
return 0;
}
else if(str.substring(0,1).equals("A")){
return 1+countA(str.substring(1));
}
else{
return countA(str.substring(1));
}
      }
}