Question

I have to count the number of unique words from a text document using Java. First I had to get rid of the punctuation in all of the words. I used the Scanner class to scan each word in the document and put in an String ArrayList.

So, the next step is where I’m having the problem! How do I create a method that can count the number of unique Strings in the array?

For example, if the array contains apple, bob, apple, jim, bob; the number of unique values in this array is 3.

---

public countWords() {
    try {
        Scanner scan = new Scanner(in);
        while (scan.hasNext()) {
            String words = scan.next();
            if (words.contains(".")) {
                words.replace(".", "");
            }
            if (words.contains("!")) {
                words.replace("!", "");
            }
            if (words.contains(":")) {
                words.replace(":", "");
            }
            if (words.contains(",")) {
                words.replace(",", "");
            }
            if (words.contains("'")) {
                words.replace("?", "");
            }
            if (words.contains("-")) {
                words.replace("-", "");
            }
            if (words.contains("‘")) {
                words.replace("‘", "");
            }
            wordStore.add(words.toLowerCase());
        }
    } catch (FileNotFoundException e) {
        System.out.println("File Not Found");
    }
    System.out.println("The total number of words is: " + wordStore.size());
}

Answer 1

Are you allowed to use Set? If so, you HashSet may solve your problem. HashSet doesn’t accept duplicates.

HashSet noDupSet = new HashSet();
noDupSet.add(yourString);
noDupSet.size();

size() method returns number of unique words.

If you have to really use ArrayList only, then one way to achieve may be,

1) Create a temp ArrayList
2) Iterate original list and retrieve element
3) If tempArrayList doesn't contain element, add element to tempArrayList