使用递归的手机文本预测（Java）

Question

I'm having some trouble on a Java assignment for school. We need to write a program that does T9 Word text prediction used by certain cell phones. It should take a user's input of numbers, find every possible combination of letters corresponding to those numbers, search a dictionary for each of those possible combinations, and display those which were found in the dictionary. Most of this program was already written for us by the professor, I just need to fill in the predictText method which does the combining of possibilities. It does the searching by calling another method that uses a recursive binary search, which I also had to fill in myself, although I'm quite certain my search method is working well. Here is my predictText method, where parameter "letter" is the letter being currently processed, parameter input is the user's input, and parameter "wordMatches" is the list of words that have been found in the dictionary.

 public static void predictText(String letter, String input, ArrayList<String> wordMatches) 
  {    
    String[] two = new String[] {"a", "b", "c"};
    String[] three = new String[] {"d", "e", "f"};
    String[] four = new String[] {"g", "h", "i"};
    String[] five = new String[] {"j", "k", "l"};
    String[] six = new String[] {"m", "n", "o"};
    String[] seven = new String[] {"p", "q", "r", "s"};
    String[] eight = new String[] {"t", "u", "v"};
    String[] nine = new String[] {"w", "x", "y", "z"};
    char firstDigit;
    String finalWord = "";

    finalWord += letter;

    if (input.equals(""))
    {
      int lookup = search(finalWord.trim());
      if (lookup != -1)
      {
        wordMatches.add(allWords[lookup]);
      }
    }

    else
    {      
      firstDigit = input.charAt(0);
      input = input.substring(1);

      if (firstDigit == '2')
      {
        for (int i = 0; i < two.length; i++)
        {
          letter = two[i];
          predictText(letter, input, wordMatches);
        }

      }
      else if (firstDigit == '3')
      {
        for (int i = 0; i < three.length; i++)
        {
          letter = three[i];
          predictText(letter, input, wordMatches);
        }

      }
      // And so forth, up to 9
    }
  }

The result that I'm getting is that it's only displaying single letters, it doesn't seem to be combining the letters into words and searching the dictionary for those complete words. Just in case some further explanation is needed, here are the assignment instructions:

"You will take the first digit from the input string, and call predictText again, once for each of the possible letters the first digit could represent, with the letter added to the variable word, and the first digit stripped from the input. For example, if the first time into predictText word is empty and input is “4663”, you would call predictText recursively 3 times with: • word as “g” and input as “663”, • word as “h” and input as “663”, • word as “i” and input as “663” The process would repeat, and you'd keep building up the word (so for word as “g” and the next digit being 6, you would recursively call with “gm”, “gn”, and “go” with the input “63”) Once there is no more input to process recursively, you've reached a base case so then call the search method to see if the word you generated exists in the dictionary. If it does, add it to the wordMatches list."

EDIT: I also thought I should include my search method code, just in case it actually is causing my problem.

public static int search(String key) 
  {
    return search(allWords, key, 0, allWords.length-1);
  }


  public static int search(String[] dictionary, String key, int start, int end) 
  {
    int middle = start + ((end - start) / 2);
    int index = -1;

    if (start > end)
    {
      index = -1;
    }
    else if (key.compareToIgnoreCase(dictionary[middle]) == 0)
    {
      index = middle;
    }
    else if (key.compareToIgnoreCase(dictionary[middle]) < 0)
    {
      index = search(dictionary, key, start, middle - 1);
    }
    else
    {
      index = search(dictionary, key, middle + 1, end);
    }

    return index;
  }

Answer 1

You're looking for only one-letter words:

String finalWord = "";

finalWord += letter;

Answer 2

Append into a String , you are doing it just for one letter word. if its unique try StringBuffer