Implement a SubstringGenerator that generates all substrings of a string. For example, the substrings of the string "rum" are the seven strings "r", "ru", "rum", "u", "um", "m", "" Hint: First enumerate all substrings that start with the first character. There are n of them if the string has length n. Then enumerate the substrings of the string that you obtain by removing the first character.

You need to supply the following class in your solution:

SubstringGenerator 

Use the following class as your tester class:

import java.util.ArrayList; import java.util.Collections; /** This program tests the substring generator. */ public class SubstringGeneratorTester { public static void main(String[] args) { SubstringGenerator generator = new SubstringGenerator("rum"); ArrayList substrings = generator.getSubstrings(); // Sort the result for checking Collections.sort(substrings); System.out.println(substrings); System.out.println("Expected: [, m, r, ru, rum, u, um]"); } }