How to make a Blank JList at a specified size? Without empty elements

Question

I am trying to create a BLANK JList for the user to see befor elements are added. Over all what is happening is I am using JFileChooser to select txt documents to be added to a list, then the vowels in each txt document are counted and displayed in the other list. The list must be visible before the user selects anything and the list must be blank. Yes there are two empty JList but obviously if I can get help with one the other is easy. So far nowhere on the internet touches on this particular subject.

Setting row count(visible) does not work, nor setsize(). Unless I am using it wrong. Please explain with examples. Thanks in advance!

An example below:

Code:

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.*;

import javax.swing.*;

public class VowelCounterApp extends JFrame implements ActionListener 
{
    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    JPanel panel1 = new JPanel();
    JPanel panel2 = new JPanel();
    JScrollPane scrollPane = new JScrollPane();
    JList selectList =  new JList();
    JList showList = new JList();
    JFileChooser fileChooser = new JFileChooser();
    JButton addFiles = new JButton("Add Files");
    JButton process = new JButton("Process");
    JButton clear = new JButton("Clear");
    JButton help = new JButton("Help");


    public VowelCounterApp()
    {
        JFrame appWindow = new JFrame("Vowel Counter");

        appWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        appWindow.setSize(1500, 600);

        appWindow.setLayout(new BorderLayout());

        appWindow.setVisible(true);

        appWindow.add(panel1, BorderLayout.WEST);
        appWindow.add(panel2, BorderLayout.EAST);


        panel1.add(selectList);
        selectList.add(scrollPane);
        panel2.add(showList);
        showList.add(scrollPane);



    }

    public void actionPerformed(ActionEvent e)
    {

    }

    public static void main(String[] args)
    {
        new VowelCounterApp();
    }

}

Hovercraft Full Of Eels · Accepted Answer · 2015-09-27T20:48:30.647

The JList API will show you two key methods:

public void setVisibleRowCount(int rowCount)
public void setPrototypeCellValue(E prototype)

So simply give your list an adequate row visible count and an adequately long enough prototype value, and then its enclosing JScrollPane's viewport will automatically size its viewport accordingly.

For example:

import java.awt.GridLayout;
import javax.swing.*;

public class JListExample extends JPanel {
    private JList<String> list1 = new JList<>();
    private JList<String> list2 = new JList<>();

    public JListExample() {
        list1.setVisibleRowCount(20);
        list2.setVisibleRowCount(20);
        list1.setPrototypeCellValue(String.format("%60s", ""));
        list2.setPrototypeCellValue(String.format("%60s", ""));

        setLayout(new GridLayout(1, 2));
        add(new JScrollPane(list1));
        add(new JScrollPane(list2));
    }

    private static void createAndShowGui() {
        JListExample mainPanel = new JListExample();

        JFrame frame = new JFrame("JList Example");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGui();
            }
        });
    }
}

Or better to avoid "magic" numbers:

public class JListExample extends JPanel {
    private static final int LIST_ROW_COUNT = 20;
    private static final int LIST_CHAR_WIDTH = 80;
    private static final String LIST_PROTOTYPE = "%" + LIST_CHAR_WIDTH + "s";
    private JList<String> list1 = new JList<>();
    private JList<String> list2 = new JList<>();

    public JListExample() {
        list1.setVisibleRowCount(LIST_ROW_COUNT);
        list2.setVisibleRowCount(LIST_ROW_COUNT);
        list1.setPrototypeCellValue(String.format(LIST_PROTOTYPE, ""));
        list2.setPrototypeCellValue(String.format(LIST_PROTOTYPE, ""));

Here, now you can see the lists better by my wrapping them and their JScrollPane in a JPanel that uses a TitledBorder:

import java.awt.BorderLayout;
import java.awt.GridLayout;
import javax.swing.*;

public class JListExample extends JPanel {
    private static final int LIST_ROW_COUNT = 20;
    private static final int LIST_CHAR_WIDTH = 80;
    private static final String LIST_PROTOTYPE = "%" + LIST_CHAR_WIDTH + "s";
    private JList<String> list1 = new JList<>();
    private JList<String> list2 = new JList<>();

    public JListExample() {
        list1.setVisibleRowCount(LIST_ROW_COUNT);
        list2.setVisibleRowCount(LIST_ROW_COUNT);
        list1.setPrototypeCellValue(String.format(LIST_PROTOTYPE, ""));
        list2.setPrototypeCellValue(String.format(LIST_PROTOTYPE, ""));

        setLayout(new GridLayout(1, 2));
        add(createListWrapper(list1, "JList 1"));
        add(createListWrapper(list2, "JList 2"));
    }

    private JComponent createListWrapper(JList<String> list, String title) {
        JScrollPane scrollPane = new JScrollPane(list);
        scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

        JPanel wrapperPanel = new JPanel(new BorderLayout());
        wrapperPanel.add(scrollPane);
        wrapperPanel.setBorder(BorderFactory.createTitledBorder(title));
        return wrapperPanel;
    }

    private static void createAndShowGui() {
        JListExample mainPanel = new JListExample();

        JFrame frame = new JFrame("JList Example");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGui();
            }
        });
    }
}

Edit
As MadProgrammer states in comment:

I'd also be careful with prototypeCellValue, unless the value matches the expected length of your data, it could truncate your data when it's displayed, just need to be careful

@user2476208: NO. You must simply **call** these two methods. — Hovercraft Full Of Eels, Sep 27 '15 at 18:47
@user2476208: and you don't add the JScrollPane to the JList, it's the other way around. You'll want to read the JList tutorial. Your use of JScrollPane is completely backwards. Check out its tutorial as well -- Just google JList tutorial and JScrollPane tutorial, first hit on both searches. Also check the API. As a general rule we kind of expect that you've looked at the intro tutorials and the API before coming here with questions as that will eliminate most overly simple questions. — Hovercraft Full Of Eels, Sep 27 '15 at 18:49
ok so JList is a generic I get that. But to set the size I would the two methods above? Example : selectList.setVisibleRowCount(12); selectList.setPrototypeCellValue(E prototype); ??? — JavaFox, Sep 27 '15 at 18:52
@user2476208: see example above, but again, please check the tut's as well. — Hovercraft Full Of Eels, Sep 27 '15 at 18:56
@user2476208: Please run the latest code so you can see clearly where the blank JLists are. — Hovercraft Full Of Eels, Sep 27 '15 at 20:14
I'd also be careful with prototypeCellValue, unless the value matches the expected length of your data, it could truncate your data when it's displayed, just need to be careful — MadProgrammer, Sep 27 '15 at 20:45
@MadProgrammer: good point. Please add an @ user24766208, so that the OP sees this as well. — Hovercraft Full Of Eels, Sep 27 '15 at 20:48
@user2476208: please see Mad's comment above. I've also added this as an edit to the answer. — Hovercraft Full Of Eels, Sep 27 '15 at 20:48
Ok your code looks good Im just trying to wrap my mind around how you used so many methods. Good Job! If you dont mind can you explain each method? Still learning over here XO — JavaFox, Sep 28 '15 at 01:36

How to make a Blank JList at a specified size? Without empty elements

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