Simple Spell Checker

Question

Hey. I'm pretty new to Java, but have to try and create a very simple spell checker. At the moment I have three classes and an interface, and I am to write a fourth and final class:
DictionaryLoader, whichprovidesastaticmethod+loadTheDictionary+which
readsthewordsfromafileandreturnsthemasanarrayofstringsinalphabetical
order.
SpellChecker, which stores the array of strings and provides a method called
check to search it. It also provides a zeroargument constructor, which calls
DictionaryLoader.loadTheDictionary.
ISpellChecker is an interface defining the check method of SpellChecker.
SpellCheckResultisaclassusedby+SpellChecker+toreturnresults.A
SpellCheckResultobjecthaspublicfieldsindicatingwhetherthewordwas
correctlyspeltand,ifnot,whatwerethewordsimmediatelybeforeandafterit.Ifit
wasbeforethefirstdictionaryentryorafterthelastonethenoneofthesefields
mightbenull.
SpellCheckerUIisaclasscontainingamainmethodwhichprovidestheuser
interfacetothesystem.
I have the code for all of these other than SpellChecker, which I have to write, except I have no clue what I'm supposed to do.
Here is the code for the four parts I have the code for:
DictionaryLoader:
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.Scanner;
import java.util.Vector;
public class DictionaryLoader {
     public static final String dictFileName="/usr/share/dict/words";
     public static String[] loadTheDictionary() {
          Scanner s;
          try {
               s = new Scanner(new BufferedReader(new FileReader(dictFileName)));
          } catch (FileNotFoundException e) {
               System.err.println("Standard dictionary file "+dictFileName+" missing");
               return new String[0];
          Vector<String> dict = new Vector<String>();
          while (s.hasNext()) {
               dict.add(s.next());
          return dict.toArray(new String[0]);
}ISpellChecker:
public interface ISpellChecker {
    /* check a word w and return a SpellCheckResult object containing
       the outcome */
     public SpellCheckResult check(String w);
}SpellCheckResult:
public class SpellCheckResult {
    public boolean correct; /* true if the word was found */
    public String before;/* if the word was not found then this field
                 * contains the dictionary word before it, or
                 * null if there isn't one, else undefined */
    public String after;/* if the word was not found then this field
                * contains the dictionary word after it, or
                * null if there isn't one, else undefined */
    public SpellCheckResult(boolean result, String before, String after) {
     this.correct = result;
     this.before = before;
     this.after = after;
}SpellCheckerUI:
import java.util.Scanner;
public class SpellCheckerUI {
      * @param args
     public static void main(String[] args) {
          // TODO Auto-generated method stub
          ISpellChecker sc = new SpellChecker();
          Scanner s = new Scanner(System.in);
          System.out.println("\n\n******SIMPLE SPELL CHECKER******\n\nEnter a word you would like to check the spelling of.\nType 'quit' to exit the program.\n");
          while (true) {
               System.out.print("Word to check: ");
               String w = s.next();
               if (w.equals("quit"))
                    break;
               SpellCheckResult r = sc.check(w);
               if (r.correct)
                    System.out.println(w+" correct");
               else
                    System.out.print(w+" was not found. Nearest neighbour(s) ");
                    if (r.before != null)
                         System.out.print(r.before+" and ");
                    if (r.after != null)
                         System.out.println(r.after);
          System.out.println("Thank you for using this program. Goodbye\n\n");
}And so far, for the SpellChecker I have:
public class SpellChecker extends SpellCheckerUI implements ISpellChecker {
     public SpellChecker() {
          DictionaryLoader.loadTheDictionary();
     public SpellCheckResult check(String w) {
          return null;
     public static void main(String[] args){
}I have no idea what code to write in the SpellChecker, so if anybody can lend a hand at all, it'd be so helpful. Thank you.

Answer 1

tad2382 wrote:
Finding the w is a little bit trickier than it seems at first. At first, it might seem that you'd want to iterate through every entry in the array...but that would be horribly inefficient. A binary search would be better: O(log(n)) runtime instead of O(n).Only with "exact matches". But the OP would also need to find "near matches": making an ordered array with a binary search worthless. A radix tree would be the way to go.
[http://en.wikipedia.org/wiki/Radix_tree]
So basically, you'd check the middle word in the array. If it's what you want return it. If it's greater (Strings implement the comparable interface, just make sure you're ignoring case), check the lower half of the array, otherwise check the upper half. Then you'd recurse and do this for the upper/lower half of the array (your recursive method would take the min & max and look at the middle element). Your base case would be that you're left with the min & max as neighboring elements in the array (and you haven't found the word)--then you have your before & after and you're all set. Just be careful you're not skipping any entries in the array with a 1 off error.
That's the pseudocode - hopefully you can figure out the java behind it.... or just get it working in a way that is the most easiest to implement. And if need be, improve it.