How do I display a list of items in a JScrollPane?

Question

First of all, I am a beginner programming student and I don't know a lot of Java/programming jargon, so if you are able to help me, please try to explain in simpler words.

I am trying to display a list of words in a JScrollPane. This list is represented by the class WordList. The JScrollPane is in another class called WordFinder.

In WordFinder, the code is something like:

WordList words = new WordList();

// (other GUI code in between)

JScrollPane scrollPane = new JScrollPane(DONT_KNOW);

If I put 'words' where DONT_KNOW is, I get a warning saying "The constructor JScrollPane(WordList) is undefined". I can understand that, a JScrollPane isn't supposed to accept this weird random class. But what do I put there then? I understand that you can put a JList in a JScrollPane, but how do I transform the WordList class into a JList (or something that JScrollPane will accept)?

I'm not sure if this helps, but here is the code in the class WordList (I didn't write this; it was given to me):

    import java.io.*;
    import java.net.URL;
    import java.text.Collator;
    import java.util.*;

    /**
     * A WordList is a set of words loaded from a file and searchable by substring.
     * A word is defined as a sequence of letters (upper case or lower case).
     * WordSets ignore alphabetic case when comparing, searching, or sorting.
     */
    public class WordList {
        private List words;

        /*
         * Rep invariant: words != null
         */

    public WordList() {

    }

    public void load(InputStream in) throws IOException {
        Collator c = Collator.getInstance();
        c.setStrength(Collator.PRIMARY);
        Set s = new TreeSet(c);

        StreamTokenizer tok = new StreamTokenizer(new InputStreamReader(in));
        tok.resetSyntax();
        tok.wordChars('a', 'z');
        tok.wordChars('A', 'Z');

        while (tok.nextToken() != StreamTokenizer.TT_EOF) {
            if (tok.ttype == StreamTokenizer.TT_WORD)
                s.add(tok.sval);
        }

        words = new ArrayList(s);
    }

    public List find(String s) {
        if (s.length() == 0) {
            return Collections.unmodifiableList(words);
        }

        s = s.toLowerCase();

        List l = new ArrayList();
        for (Iterator i = words.iterator(); i.hasNext();) {
            String word = (String) i.next();
            if (word.toLowerCase().indexOf(s) != -1)
                l.add(word);
        }
        return l;
    }

    /**
     * Main method. Demonstrates how to use this class.
     * 
     * @param args
     *            Command-line arguments. Ignored.
     */
    public static void main(String[] args) {
        WordList words = new WordList();

        // Create the word list from a resource.
        // The words file must be in the same directory (or jar file directory)
        // as this class.
        URL url = WordList.class.getResource("words.txt");
        if (url == null)
            throw new RuntimeException("Missing resource: words");
        try {
            words.load(url.openStream());
        } catch (IOException e) {
            throw new RuntimeException(e);
        }

        // Print all the words containing "ph"
        List matches = words.find("holst");
        for (Iterator i = matches.iterator(); i.hasNext();) {
            System.out.println(i.next());
        }
    }
}

Answer 1

Use JList inside the JScrollPane.

Here's the example.

    JList list;
    DefaultListModel listModel;
    listModel = new DefaultListModel();
    listModel.addElement("word1");
    listModel.addElement("word2");
    listModel.addElement("word3");

    //Create the list and put it in a scroll pane.
    list = new JList(listModel);
    list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
    list.setSelectedIndex(0);
    list.addListSelectionListener(this);
    list.setVisibleRowCount(5);
    JScrollPane listScrollPane = new JScrollPane(list);

The above example is from ListDemo.java

Checkout Oracle's tutorial on JList.

Answer 2

Assuming your word is described by Word class and you have List<Word> (i.e. java.util.List<>) of words;

You have to create list model which will be model for JList;

something like:

    // you have list of words - wordList
    List<Word> wordList= new ArrayList<Word>();

    // create list model for JList
    DefaultListModel<Word> model = new DefaultListModel<Word>();
    // add all words from wordList to model
    for(Word word : wordList){
        model.addElement(word);
    }

    // create JList with model - model
    JList<Word> list = new JList<Word>(model);

   // create scroll pane for scrolling JList
    JScrollPane scrollPane = new JScrollPane(list);

If your word is instance of String, you can replace all Word by String.

One more tip, you may have directly created list model (DefaultListModel<>) for storing list of words instead of java.util.List<>. So you will not have to maintain two lists (DefaultListModel<> and java.util.List<>).

Answer 3

I think your custom class WordList should inherit JList to make it work (a.e put as parameter to JScrollPane).

Something like:

public class WordList extends JList<Object> {....}

After you can write:

 WordList words = new WordList();

 JScrollPane scrollPane = new JScrollPane(words);