A class to find the words from a sentence that is a concatenation of the permutation of the words

Tokenizer.java

package com.ferhatelmas;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;

public class Tokenizer {

  private HashMap<String, String> dict;

  public Tokenizer(String[] words) {
    this.dict = new HashMap<String, String>();

    for(String word : words)
      dict.put(sorted(word), word);
  }

  public static String sorted(String w) {
    char[] chars = w.toCharArray();
    Arrays.sort(chars);
    return new String(chars);
  }

  public List<String> getWords(String sentence) {

    if(sentence.isEmpty()) return new ArrayList<String>();

    List<String> words = new ArrayList<String>();
    int len = sentence.length();
    for(int i=1; i<=len; i++) {
      String token = sorted(sentence.substring(0, i));
      if(dict.containsKey(token)) {
        List<String> found = getWords(sentence.substring(i));

        if(found != null) {
          words.add(dict.get(token));
          words.addAll(found);
          break;
        }
      }
    }

    return words.size() == 0 ? null : words;
  }

  public static void main(String[] args) {
    Tokenizer t = new Tokenizer(new String[] {"ferhat", "elmas", "huseyn", "gasimov", "that", "is", "a", "sample"});
    List<String> words = t.getWords("usnyehttahsiaaspmle");
    if(words != null) // unmatched returns null since empty string returns empty list
      for(String w : words)
        System.out.println(w);
  }
}