How to Store objects in an ArrayList when you do not know how many object you need to create?

Question

Back ground: I am pairing up two pieces of data, both Strings, into an ArrayList. Therefore I am storing the paired data into an object, and then storing this object into an ArrayList. I have a text file that for each word, I am assigning a number to. The paired data is then word-number (but I have typed them both as String). I do not know how many objects I will need for any given file size.

How do I set up a logic to iterate through the text file and populate my ArrayList. This is what I have done so far:

The : PredictivePrototype.wordToSignature(aWord)// converts the word into a number signature e.g "4663" for a word like "home"

public class ListDictionary {

    private static ArrayList<WordSig> dictionary;

    public ListDictionary() throws FileNotFoundException {

        File theFile = new File("words");
        Scanner src = new Scanner(theFile);

        while (src.hasNext()) {
            String aWord = src.next();
            String sigOfWord = PredictivePrototype.wordToSignature(aWord);

            // assign each word and its corresponding signature into attribute
            // of an object(p) of class WordSig.
            //WordSig p1 = new WordSig(aWord, sigOfWord);

            //Then add this instance (object) of class Wordsig into ArrayList<WordSig>
            dictionary.add(new WordSig(aWord, sigOfWord));
        }
        src.close();


    }

Other class to which paired data is stored:

public class WordSig {

    private String words;
    private String signature;

    public WordSig(String words, String signature) {
        this.words=words;
        this.signature=signature;

    }

}

That's the beauty of `ArrayList`, you can keep adding to it, it will resize itself. — Sotirios Delimanolis, Feb 13 '14 at 08:01
I know, but I do not know how generate more objects iterativley... — user3274549, Feb 13 '14 at 08:01
What do you think you are currently doing in your `while` loop? — Sotirios Delimanolis, Feb 13 '14 at 08:02
In particular, you seem to be doing it already - so what's not working with the code you've got? — Jon Skeet, Feb 13 '14 at 08:03
so this code for adding x object into the arraylist is ok?dictionary.add(new WordSig(aWord, sigOfWord)); — user3274549, Feb 13 '14 at 08:03
You have to initialize the arraylist 'private static ArrayList dictionary = new ArrayList();' but the rest is OK, I think. I don't undestand your problem, really. — luanjot, Feb 13 '14 at 08:03
I am presently getting the following list of errors when I try and print out the arrayList: WordSig@3aeaf2d9 — user3274549, Feb 13 '14 at 08:09
That's not an error, that's the default string represenation of an object. If you want it to be something different, you'll have to override `toString()` in your `WordSig` class. See http://stackoverflow.com/questions/3615721/how-to-use-the-tostring-method-in-java — André Stannek, Feb 13 '14 at 08:15

score 0 · Answer 1 · answered Feb 13 '14 at 08:49

Your code seems to be OK. With ArrayList you can add as many elements as you want (by using add() function).

Here is an example:

import java.util.ArrayList;

public class ListDictionary {

    public class WordSig {
        private String words;
        private String signature;

        public WordSig(String words, String signature) {
            this.words=words;
            this.signature=signature;
        }
        public String getWords() {
            return words;
        }
        public String getSignature() {
            return signature;
        }
    }

    private static ArrayList<WordSig> dictionary = new ArrayList<WordSig>();

    public ListDictionary() {
        // add as many as you want
        for ( int i=0; i < 10; i++)
            dictionary.add(new WordSig("key"+i, "value"+i));
    }

    public static class testListDictionary {
        public static void main(String[] args) {
            new ListDictionary();
            // test output
            for ( int i=0; i < dictionary.size(); i++ )
                System.out.println( "<" + dictionary.get(i).getWords() + "|"
                                    + dictionary.get(i).getSignature() + ">");
        }
    }
}

How to Store objects in an ArrayList when you do not know how many object you need to create?

1 Answers1