Nsryjdtyk

I would like to read through a a text document and then add only the unique words to the arraylist of "Word" objects. It appears that the code I have now does not enter any words at all into the wordList arraylist.

public ArrayList<Word> wordList = new ArrayList<Word>();

    String fileName, word;

    int counter;

    Scanner reader = null;

    Scanner scanner = new Scanner(System.in);



try {

            reader = new Scanner(new FileInputStream(fileName));

        }

        catch(FileNotFoundException e) {

            System.out.println("The file could not be found. The program will now exit.");

            System.exit(0);

        }



    while (reader.hasNext()) {

                word = reader.next().toLowerCase();

                for (Word value : wordList) {

                    if(value.getValue().contains(word)) {

                        Word newWord = new Word(word);

                        wordList.add(newWord);

                    }

                }

                counter++;

            }



    public class Word {



        String value;

        int frequency;



        public Word(String v) {

            value = v;

            frequency = 1;

        }



        public String getValue() {

            return value;

        }



    public String toString() {

        return value + " " + frequency;

    }



}

Alright, let's start by fixing your current code. The issue you have is that you are only adding a new word object to the list when one already exists. Instead, you need to add a new Word object when none exist, and increment the frequency otherwise. Here is an example fix for that:

    ArrayList<Word> wordList = new ArrayList<Word>();

    String fileName, word;

    Scanner reader = null;

    Scanner scanner = new Scanner(System.in);



    try {

        reader = new Scanner(new FileInputStream(fileName));

    }

    catch(FileNotFoundException e) {

        System.out.println("The file could not be found. The program will now exit.");

        System.exit(0);

    }



    while (reader.hasNext()) {

            word = reader.next().toLowerCase();

            boolean wordExists = false;

            for (Word value : wordList) {

               // We have seen the word before so increase frequency.

               if(value.getValue().equals(word)) {

                    value.frequency++;

                    wordExists = true;

                    break;

               }

            }

            // This is the first time we have seen the word!

            if (!wordExists) {

                Word newValue = new Word(word);

                newValue.frequency = 1;

                wordList.add(newValue);

             }

        }

}

However, this is a really bad solution (O(n^2) runtime). Instead we should be using datastructure known as a Map which will bring our runtime down to (O(n))

    ArrayList<Word> wordList = new ArrayList<Word>();

    String fileName, word;

    int counter;

    Scanner reader = null;

    Scanner scanner = new Scanner(System.in);



    try {

        reader = new Scanner(new FileInputStream(fileName));

    }

    catch(FileNotFoundException e) {

        System.out.println("The file could not be found. The program will now exit.");

        System.exit(0);

    }

    Map<String, Integer> frequencyMap = new HashMap<String, Integer>();

    while (reader.hasNext()) {

       word = reader.next().toLowerCase();

       // This is equivalent to searching every word in the list via hashing (O(1))

       if(!frequencyMap.containsKey(word)) {

          frequencyMap.put(word, 1);

       } else {

          // We have already seen the word, increase frequency.

          frequencyMap.put(word, frequencyMap.get(word) + 1);

       } 

    }



    // Convert our map of word->frequency to a list of Word objects.

    for(Map.Entry<String, Integer> entry : frequencyMap.entrySet()) {

      Word word = new Word(entry.getKey());

      word.frequency = entry.getValue();

      wordList.add(word);

    }

}

Your for-each loop is iterating over wordList, but that is an empty ArrayList so your code will never reach the wordList.add(newWord); line

I appreciate that perhaps you wanted critique on why your algorithm wasn't working, or maybe it was an example of a much larger problem but if all you want to do is count occurences, there is a much simpler way of doing this.

Using Streams in Java 8 you can boil this down to one method - create a Stream of the lines in the file, lowercase them and then use a Collector to count them.

public static void main(final String args) throws IOException

{

    final File file = new File(System.getProperty("user.home") + File.separator + "Desktop" + File.separator + "myFile.txt");



    for (final Entry<String, Long> entry : countWordsInFile(file).entrySet())

    {

        System.out.println(entry);

    }

}



public static Map<String, Long> countWordsInFile(final File file) throws IOException

{

    return Files.lines(file.toPath()).map(String::toLowerCase).collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

}

I've not done anything with Streams until now so any critique welcome.