Converting ArrayList to Hashset in java

Question

I have this code that reads and counts every word in a txt file, however I only want it to count each word on a line once, and so I'm trying to create a HashSet however I'm having trouble converting an ArrayList to a HashSet. Here's my code:

try {
    List<String> list = new ArrayList<String>();
    int totalWords = 0;
    int uniqueWords = 0;
    File fr = new File("filename.txt");
    Scanner sc = new Scanner(fr);
    while (sc.hasNext()) {
        String words = sc.next();
        String[] space = words.split(" ");
        Set<String> set = new HashSet<String>(Arrays.asList(space));
        for (int i = 0; i < set.length; i++) {
            list.add(set[i]);
        }
        totalWords++;
    }
    System.out.println("Words with their frequency..");
    Set<String> uniqueSet = new HashSet<String>(list);
    for (String word : uniqueSet) {
        System.out.println(word + ": " + Collections.frequency(list,word));
    }
} catch (Exception e) {

    System.out.println("File not found");

  }  

If anyone could help on why length "cannot be resolved or is not a field", and also why I have an error on "set[i]" telling me it must be resolved to a String. Thank you

Answer 1

I have used a map data structure to store and update the words and their respective frequencies..

As per your requirement: Each word should be counted just once even though they appear multiple times in a single line.

Iterate over the each line:

 Store all the words in the set.

 Now just iterate over this set and update the map data structure.

Hence, at last the values corresponding to the word in the map will be the required frequencies.

You can look at my code below:

import java.io.File;
import java.util.*;

public class sol {
    public static void main(String args[]) {
        try {
            File fr = new File("file.txt");
            Scanner sc = new Scanner(fr);

            // to maintain frequency of each word after reading each line..
            HashMap<String, Integer> word_frequency = new HashMap<String, Integer>();

            while(sc.hasNextLine()) {
                // input the line..
                String line = sc.nextLine();
                String words[] = line.split(" ");

                // just store which unique words are there in this line..
                HashSet<String> unique_words = new HashSet<String>();

                for(int i=0;i<words.length;i++) {
                    unique_words.add(words[i]);     // add it to set..
                }

                // Iterate on the set now to update the frequency..
                Iterator itr = unique_words.iterator();

                while(itr.hasNext()) {
                    String word = (String)itr.next();   

                    // If this word is already there then just increment it..
                    if(word_frequency.containsKey(word)) {
                        int old_frequency = word_frequency.get(word);
                        int new_frequency = old_frequency + 1;
                        word_frequency.put(word, new_frequency);
                    }
                    else {
                        // If this word is not there then put this 
                        // new word in the map with frequency 1..

                        word_frequency.put(word, 1);
                    }
                }
            }

            // Now, you have all the words with their respective frequencies..
            // Just print the words and their frequencies..
            for(Map.Entry obj : word_frequency.entrySet()) {
                String word = (String)obj.getKey();
                int frequency = (Integer)obj.getValue();

                System.out.println(word+": "+frequency);
            }
        }
        catch(Exception e) {
            // throw whatever exception you wish.. 
        }
    }
}

Answer 2

As you have been told in comments , you cannot use [] nor length as any Set is a Collection and not an array:

You could try this way:

try {
    List<String> list = new ArrayList<String>();
    int totalWords = 0;
    int uniqueWords = 0;
    File fr = new File("filename.txt");
    Scanner sc = new Scanner(fr);
    while (sc.hasNext()) {
         String words = sc.next();
         String[] space = words.split(" ");
         Set<String> set = new HashSet<String>(Arrays.asList(space));
         for(String element : set){
              list.add(element);
         }
         totalWords++;
    }
    System.out.println("Words with their frequency..");
    Set<String> uniqueSet = new HashSet<String>(list);
    for (String word : uniqueSet) {
         System.out.println(word + ": " + Collections.frequency(list,word));
    }
} catch (Exception e) {
    System.out.println("File not found");
}