Find minimum distance between words

/* This class will be given a list of words (such as might be tokenized
 * from a paragraph of text), and will provide a method that takes two
 * words and returns the shortest distance (in words) between those two
 * words in the provided text. 
 * Example:
 *   WordDistanceFinder finder = new WordDistanceFinder(Arrays.asList("the", "quick", "brown", "fox", "quick"));
 *   assert(finder.distance("fox","the") == 3);
 *   assert(finder.distance("quick", "fox") == 1);
 * /

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O(n) complexity and O(1) space complexity.

public class DistanceFinder {
 public int WordDistance(String[] words, String word1, String word2) {
  if (words == null || word1 == null || word2 == null) 
   throw new NullPointerException("Null array or words");
  if (words.length == 0)
   return Integer.MAX_VALUE;
  if (word1.equals(word2))
   return 0;
  int index1 = -1;
  int index2 = -1;
  int minDistance = Integer.MAX_VALUE;
  for (int i = 0; i < words.length; i++) {
   if (words[i] == word1) {
    index1 = i;
   }
   if (words[i] == word2) {
    index2 = i;
   }
   if ((words[i] == word1 || words[i] == word2) && (index1 != -1 && index2 != -1)) {
    minDistance = Math.min(minDistance, Math.abs(index1 - index2));
   }
  }
  if (index1 == -1 && index2 == -1)
   throw new IllegalArgumentException ("Cannot find the word!");
  return minDistance; 
 }

}