Question

This is a homework question that I am having a bit of trouble with.

Write a recursive method that determines if a String is a hex number.
Write javadocs for your method.
A String is a hex number if each and every character is either
0 or 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9
or a or A or b or B or c or C or d or D or e or E or f or f.

At the moment all I can see to test this is if the character at 0 of the string is one of these values he gave me then that part of it is a hex.

Any hints or suggestions to help me out?

This is what I have so far: `

public boolean isHex(String string){


    if (string.charAt(0)==//what goes here?){
        //call isHex again on s.substring(1)
    }else return false;
    }

`

Answer 1

Since this is homework, I only give some hints instead of code:

Write a method that always tests the first character of a String if it fulfills the requirements. If not, return false, if yes, call the method again with the same String, but the first character missing. If it is only 1 character left and it is also a hex character then return true.

Pseudocode:

public boolean isHex(String testString) {


   If String has 0 characters -> return true;

   Else

      If first character is a hex character -> call isHex with the remaining characters

      Else if the first character is not a hex character -> return false;

}