Storing JList selections in an array String[] in Java

Question

I am creating a GUI, and can't figure out how to store the JList user selections in an array. I tried List<<Sting>>, Object[] etc... JRadioButtons and other GUIs are fine, only JList is not working...

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

public class Test extends JFrame {

    private JTextField num3;
    private JLabel label3;
    private JButton button;
    private JRadioButton radio2;
    private JRadioButton radio3;
    private ButtonGroup radioGroup;

    private JList statesList;

    String[] states = {"Alabama",   "Alaska",   "Wyoming"};
    String expression;
    String frequency;

    // no args constructor
    public Test() {
        createUI();
    }
    private void createUI() {
        Container contentPane = getContentPane();
        contentPane.setLayout(null);

        label3 = new JLabel();
        label3.setText("Search Expression");
        label3.setBounds(16, 120, 200, 21);
        contentPane.add(label3);
        num3 = new JTextField();
        num3.setText("(any expression)");
        num3.setBounds(16, 144, 150, 21);
        num3.setHorizontalAlignment(JTextField.LEFT);
        contentPane.add(num3);

        button = new JButton("Start!");
        button.setBounds(90,430,126,24);
        contentPane.add(button);
        button.addActionListener(
                new ActionListener() {
                public void actionPerformed(ActionEvent event)
                {
                    buttonActionPerformed(event);
                }
                }
                );
        // States Selection
        statesList = new JList(states);
        statesList.setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);
        statesList.setVisibleRowCount(5);
        statesList.setBounds(400, 16, 100, 50);
        JScrollPane statesScroll = new JScrollPane(statesList);
        statesScroll.setBounds(180, 16, 135, 400);
        contentPane.add(statesScroll);

        // Radio Buttons
        radio2 = new JRadioButton();
        radio3 = new JRadioButton();
        radio3.setSelected(true);

        radioGroup = new ButtonGroup();
        radioGroup.add(radio2);
        radioGroup.add(radio3);

        radio2.setText("Quarterly");
        radio3.setText("Yearly");

        radio2.setBounds(16,360,90,23);
        radio3.setBounds(16,385,75,23);

        contentPane.add(radio2);
        contentPane.add(radio3);

        // set the content Pane window
        setTitle("Search Engine");
        setSize(750,500);
        setVisible(true);

        }

    // Getting the user's TextField and JRadioButton input
    private void buttonActionPerformed(ActionEvent event) {
        expression = num3.getText();
        if (radio2.isSelected())
                frequency = "quarterly";
        else frequency = "yearly";
        System.out.println(expression+","+frequency);


    // The above "expression" and "frequency" work fine. But JList does not 
    // work. What am I doing wrong? I tried Object[] instead of List<String>...

        List<String> values = statesList.getSelectedValues();
        return values==null ? null : values.toArray(new String[values.size()]);
        }


    // main thread
    public static void main(String[] args) {
        Test application = new Test();
        application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        }
}

Are you sure that you are selecting your JList items before getting selected items? — Arsen Alexanyan, Feb 28 '13 at 17:52

score 2 · Accepted Answer · edited May 23 '17 at 12:27

This variant iterates the Object[] returned by getSelectedValues() to show expected values in the console. Next thing to fix is the layouts.

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

//public class Test extends JFrame {
public class Test {

    private JTextField num3;
    private JLabel label3;
    private JButton button;
    private JRadioButton radio2;
    private JRadioButton radio3;
    private ButtonGroup radioGroup;

    private JList statesList;

    String[] states = {"Alabama",   "Alaska",   "Wyoming"};
    String expression;
    String frequency;

    // no args constructor
    public Test() {
        createUI();
    }

    private void createUI() {
        JFrame f = new JFrame("Search Engine");
        Container contentPane = f.getContentPane();
        // This needs fixing NEXT!
        contentPane.setLayout(null);

        label3 = new JLabel();
        label3.setText("Search Expression");
        label3.setBounds(16, 120, 200, 21);
        contentPane.add(label3);
        num3 = new JTextField();
        num3.setText("(any expression)");
        num3.setBounds(16, 144, 150, 21);
        num3.setHorizontalAlignment(JTextField.LEFT);
        contentPane.add(num3);

        button = new JButton("Start!");
        button.setBounds(90,430,126,24);
        contentPane.add(button);
        button.addActionListener(
            new ActionListener() {
                public void actionPerformed(ActionEvent event) {
                    buttonActionPerformed(event);
                }
            });
        // States Selection
        statesList = new JList(states);
        statesList.setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);
        statesList.setVisibleRowCount(5);
        statesList.setBounds(400, 16, 100, 50);
        JScrollPane statesScroll = new JScrollPane(statesList);
        statesScroll.setBounds(180, 16, 135, 400);
        contentPane.add(statesScroll);

        // Radio Buttons
        radio2 = new JRadioButton();
        radio3 = new JRadioButton();
        radio3.setSelected(true);

        radioGroup = new ButtonGroup();
        radioGroup.add(radio2);
        radioGroup.add(radio3);

        radio2.setText("Quarterly");
        radio3.setText("Yearly");

        radio2.setBounds(16,360,90,23);
        radio3.setBounds(16,385,75,23);

        contentPane.add(radio2);
        contentPane.add(radio3);

        // set the content Pane window
        f.setSize(750,500);
        //f.pack();
        f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        f.setLocationByPlatform(true);
        f.setVisible(true);
    }

    // Getting the user's TextField and JRadioButton input
    private void buttonActionPerformed(ActionEvent event) {
        expression = num3.getText();
        if (radio2.isSelected())
            frequency = "quarterly";
        else frequency = "yearly";
        System.out.println(expression+","+frequency);

        Object[] values = statesList.getSelectedValues();
        for (Object state : values) {
            System.out.println(state);
        }
    }


    // main thread
    public static void main(String[] args) {
        Runnable r = new Runnable() {

            @Override
            public void run() {
                Test application = new Test();
            }
        };
        // Swing GUIs should be created and updated on the EDT
        // http://docs.oracle.com/javase/tutorial/uiswing/concurrency/initial.html
        SwingUtilities.invokeLater(r);
    }
}

Tips

Don't extend frame, just use an instance.
J2SE GUIs (Swing & AWT) should be created and updated on the EDT. See Concurrency in Swing - Initial Threads especially.
contentPane.setLayout(null); This will not work in the real world (read probably the next PC as 'the real world'). Use layout managers for a robust GUI. See Laying Out Components Within a Container for details, and also this nested layout example for grouping layouts according to need.

yourdeveloperfriend · Answer 2 · 2013-02-28T22:18:47.017

0

According to the documentation, getSelectedValues returns an object array.

Object[] values = statesList.getSelectedValues();

If you're positive they're all strings, you can just type cast them.

String[] values = (String[]) statesList.getSelectedValues();

Edit: Try this:

Object[] values = statesList.getSelectedValues();
String[] strings = new String[values.length];
for(int i = 0; i < values.length; i++) {
  if(values[i] instanceof String) {
    strings[i] = ((String) values[i]);
  }
}

edited Feb 28 '13 at 22:18

answered Feb 28 '13 at 17:56

yourdeveloperfriend

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I know it returns an object array. I tried all those variations. Actually, I am able to print to console: Object[] values = statesList.getSelectedValues(); System.out.println(values[0]); //But the problem is that I cannot store the selected values in an array. I read the documentation many times... – Buras Feb 28 '13 at 18:31

Storing JList selections in an array String[] in Java

2 Answers2

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