Comparing two String arrays

Question

I'm making a program that compares two text files and returns their similarity (based on a given algorithm). For each unique word in the first file, I want to find the probabilities that they occur in the second file. But whenever I run my program the similarity returned is always 0.0. This is what I have right now:

public static double nestedLoop(String[] doc1, String[] doc2) {
 // nested loop: sort doc1, for each unique word in doc1, find all
 // occurences in doc2 using a sequential search
 java.util.Arrays.sort(doc1);
 double similarity = 0.0;
 for (int i = 0; i < doc1.length - 1; i++) {
 if (doc1[i] != doc1[i + 1]) {
 String unique = doc1[i];
 double count = 0.0;
 for (int j = 0; j < doc2.length; j++) {
 if (unique == doc2[j]) {
 count++;
 similarity += count / doc2.length;
 }
 }
 }
 }
 return similarity;
}

Can someone tell me what is going on?

Answer 1

if (unique == doc2[j]) {

should be

if (unique.equals(doc2[j])) {

Same for if (doc1[i] != doc1[i + 1]) {

should be:

 if (!(doc1[i].equals(doc1[i + 1]))) {

String comparison should always use equals() instead of == (except case of String literal comparison)

Please read How do I compare strings in Java?

• yiwei: WOOOOOW I am stupid. I've definitely run into this before. I'll give it a try. Thanks!
• yiwei: actually, one more small question. If I have to use equals() for String comparison, how come in the first if statement I can use the != to compare doc1[i] and doc[i + 1]? Aren't they also Strings?
• kosa: @59eagle: Valid question, yes you need to use .equals() there also.
• kosa: @ColinD: Added clarification.