Infinite Loop Iterating Through Hashtable

Question

I'm trying find the most popular word in an array using Hashtables. For some reason the while loop is looping infinitely. I've debugged and the element never changes from the first one it gets. Any ideas on why this is happening?

Here is my code:

import java.util.Hashtable;

public class MyClass {
  public String mostPopularString (String []words) {
    if (words == null)
            return null;
    if (words.length == 0)
            return null;
    Hashtable<String, Integer> wordsHash = new Hashtable<String, Integer>();
    for (String thisWord : words)
    {
        if (wordsHash.containsKey(thisWord))
        {
            wordsHash.put(thisWord, wordsHash.get(thisWord) + 1);
        }
        else
        {
            wordsHash.put(thisWord, 1);
        }
    }
    Integer mostPopularCount = 0;
    String mostPopularWord = null;
    boolean tie = false;
    while (wordsHash.keys().hasMoreElements())
    {
        String currentWord = (String) wordsHash.keys().nextElement();
        if (wordsHash.get(currentWord) > mostPopularCount)
        {
            mostPopularCount = wordsHash.get(currentWord);
            mostPopularWord = currentWord;
            tie = false;
        }
        else if (wordsHash.get(currentWord) == mostPopularCount)
        {
            tie = true;
        }
    }
    if (tie)
        return null;
    else
        return mostPopularWord;
  }
}

Answer 1

You're calling wordsHash.keys() on each iteration of the loop, which gives you a fresh Enumeration<String> on each iteration - you're then calling it again inside the loop.

You want to call it once, and then iterate over the single Enumeration<String>:

Enumeration<String> iterator = wordsHash.keys();
while (iterator.hasMoreElements())
{
    String currentWord = iterator.nextElement();
    ...
}

Note that as you're also getting the value for each element, you'd be better off iterating over the entrySet() rather than the keys().

You'd also be better off using HashMap instead of Hashtable, as then you could just use an enhanced for loop...