Implement a SubstringGenerator class that generates all substrings of a string recursively. (JAVA)

For example, the substrings of the string rum are the seven strings: rum, ru, r, um, u, 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.

Here is what your output should look like after your project is completed. (The order of your substrings is not important, as long as your generator produces all substrings correctly).

Substrings of "ab"

Actual: '' 'b' 'a' 'ab'

Expected: '' 'b' 'a' 'ab'

Substrings of "abc"

Actual: '' 'c' 'b' 'bc' 'a' 'ab' 'abc'

Expected: '' 'c' 'b' 'bc' 'a' 'ab' 'abc'

Substrings of "abc123"

Actual: '' '3' '2' '23' '1' '12' '123' 'c' 'c1' 'c12' 'c123' 'b' 'bc' 'bc1' 'bc12' 'bc123' 'a' 'ab' 'abc' 'abc1' 'abc12' 'abc123'

Expected: '' '3' '2' '23' '1' '12' '123' 'c' 'c1' 'c12' 'c123' 'b' 'bc' 'bc1' 'bc12' 'bc123' 'a' 'ab' 'abc' 'abc1' 'abc12' 'abc123'

The issue I am having is with the starter code I was given:

import java.util.ArrayList;

public class SubstringGenerator { public static ArrayList getSubstrings(String word) { //this is the value you will return ArrayList result = new ArrayList(); //come up with a base case first // Below here is the recursive case // Form a simpler word by removing the first character

// Generate all substrings of the simpler word // This is where you will make a recursive call // You can store the result from this temporary call in // your results ArrayList

// Add all strings that start with word.charAt(0) // You will need a loop here // Return all substrings return result; } }

I can't seem to find any answer of how to do it through an arraylist method This is the given tester method as well:

import java.util.ArrayList;

public class SubstringTester { public static void main(String[] args) { ArrayList substrings = SubstringGenerator.getSubstrings("ab"); System.out.println("Substrings of \"ab\""); System.out.print("Actual: "); for (String s : substrings) { System.out.print("'" + s + "' "); } System.out.println(); System.out.println("Expected: '' 'b' 'a' 'ab'"); System.out.println(); substrings = SubstringGenerator.getSubstrings("abc"); System.out.println("Substrings of \"abc\""); System.out.print("Actual: "); for (String s : substrings) { System.out.print("'" + s + "' "); } System.out.println(); System.out.println("Expected: '' 'c' 'b' 'bc' 'a' 'ab' 'abc'"); System.out.println(); substrings = SubstringGenerator.getSubstrings("rum"); System.out.println("Substrings of \"rum\""); System.out.print("Actual: "); for (String s : substrings) { System.out.print("'" + s + "' "); } System.out.println(); System.out.println("Expected: '' 'm' 'u' 'um' 'r' 'ru' 'rum'"); System.out.println(); System.out.println("Substrings of \"abc123\""); substrings = SubstringGenerator.getSubstrings("abc123"); System.out.print("Actual: "); for (String s : substrings) { System.out.print("'" + s + "' "); } System.out.println(); System.out.println("Expected: '' '3' '2' '23' '1' '12' '123' 'c' 'c1' 'c12' 'c123' 'b' 'bc' 'bc1' 'bc12' 'bc123' 'a' 'ab' 'abc' 'abc1' 'abc12' 'abc123'"); } }