Substring using recursion

Question

I'm trying to implement my own substring (fromIndex, toIndex) function using recursion. I have tried several ways of doing this, but there are still errors. Can someone help me with this? This is my code so far:

String s;
    RecursiveString(String myS){
        s=myS;
    }
String subString(int from, int to) {
        if(this.s.isEmpty())return "hi";
        else if(from==this.s.length()-1)return "";
        else if(from==to)return "error";
        return this.subString(from+1, to);
    }

example:

public static void main(String[] args) {
        RecursiveString rs=new RecursiveString("abcesf");
        System.out.println(rs.subString(2, 4));
    }

output: "error"

Answer 1

This solution works for recursive

public class HelloWorld{

     public static void main(String []args){
        System.out.println("Hello World");
     
     RecursiveString.s = "HelloWorld";
        System.out.println(RecursiveString.subString(0,3));
        
     }
     public static class RecursiveString {
        public static String s;
        
        public static  String subString(int from, int to) {
            if(s.isEmpty())return "hi";
            else if(from==s.length()-1)return "";
            else if(from==to)return "";
            return s.charAt(from) + subString(from+1, to);
    }
}
}

OUTPUT:

Hello World
Hel