Source code snippets (examples)

This is a list of Alvin Alexander's source code snippets (simple source code examples).

Java/Scala JOptionPane examples

These are some simple Java/Scala JOptionPane examples in the form of a Scala utility class (an object, actually).

package com.alvinalexander.cato.utils

import javax.swing.JTextArea
import javax.swing.JScrollPane
import javax.swing.JOptionPane

object GuiUtils {

    def showErrorDialog(title: String, textToDisplay: String) {
        JOptionPane.showMessageDialog(
            null,
            textToDisplay,
            title,
            JOptionPane.ERROR_MESSAGE)
    }

    def showErrorDialogWithLongText(title: String, textToDisplay: String) {
        JOptionPane.showMessageDialog(
            null,
            createTextareaWidgetInsideScrollPane(textToDisplay),
            title,
            JOptionPane.ERROR_MESSAGE)
    }

    def createTextareaWidgetInsideScrollPane(text: String): JScrollPane = {
        val textArea = new JTextArea(20, 70)
        textArea.setText(text)
        textArea.setCaretPosition(0)
        textArea.setEditable(false)
        new JScrollPane(textArea)
    }
    

}

These methods make it easy to display error, warning, and informational messages in dialogs in Swing applications.

Source code for a Java SwingWorker with ProgressBar example (SwingWorker background thread)

Here's the source code for a Java SwingWorker with ProgressBar example from Sun:

/**
 * Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Sun Microsystems nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

import java.awt.BorderLayout;
import java.awt.Cursor;
import java.awt.Insets;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.util.Random;

import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JProgressBar;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingWorker;
public class ProgressBarDemo extends JPanel implements ActionListener,
    PropertyChangeListener {

  private JProgressBar progressBar;
  private JButton startButton;
  private JTextArea taskOutput;
  private Task task;

  class Task extends SwingWorker<Void, Void> {
    /**
     * Main task. Executed in background thread.
     */
    @Override
    public Void doInBackground() {
      Random random = new Random();
      int progress = 0;
      // Initialize progress property.
      setProgress(0);
      while (progress < 100) {
        // Sleep for up to one second.
        try {
          Thread.sleep(random.nextInt(1000));
        } catch (InterruptedException ignore) {
        }
        // Make random progress.
        progress += random.nextInt(10);
        setProgress(Math.min(progress, 100));
      }
      return null;
    }

    /**
     * Executed in event dispatching thread
     */
    @Override
    public void done() {
      Toolkit.getDefaultToolkit().beep();
      startButton.setEnabled(true);
      setCursor(null); // turn off the wait cursor
      taskOutput.append("Done!\n");
    }
  }

  public ProgressBarDemo() {
    super(new BorderLayout());

    // Create the demo's UI.
    startButton = new JButton("Start");
    startButton.setActionCommand("start");
    startButton.addActionListener(this);

    progressBar = new JProgressBar(0, 100);
    progressBar.setValue(0);
    progressBar.setStringPainted(true);

    taskOutput = new JTextArea(5, 20);
    taskOutput.setMargin(new Insets(5, 5, 5, 5));
    taskOutput.setEditable(false);

    JPanel panel = new JPanel();
    panel.add(startButton);
    panel.add(progressBar);

    add(panel, BorderLayout.PAGE_START);
    add(new JScrollPane(taskOutput), BorderLayout.CENTER);
    setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));

  }

  /**
   * Invoked when the user presses the start button.
   */
  public void actionPerformed(ActionEvent evt) {
    startButton.setEnabled(false);
    setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));
    // Instances of javax.swing.SwingWorker are not reusuable, so
    // we create new instances as needed.
    task = new Task();
    task.addPropertyChangeListener(this);
    task.execute();
  }

  /**
   * Invoked when task's progress property changes.
   */
  public void propertyChange(PropertyChangeEvent evt) {
    if ("progress" == evt.getPropertyName()) {
      int progress = (Integer) evt.getNewValue();
      progressBar.setValue(progress);
      taskOutput.append(String.format("Completed %d%% of task.\n", task
          .getProgress()));
    }
  }

  /**
   * Create the GUI and show it. As with all GUI code, this must run on the
   * event-dispatching thread.
   */
  private static void createAndShowGUI() {
    // Create and set up the window.
    JFrame frame = new JFrame("ProgressBarDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    // Create and set up the content pane.
    JComponent newContentPane = new ProgressBarDemo();
    newContentPane.setOpaque(true); // content panes must be opaque
    frame.setContentPane(newContentPane);

    // Display the window.
    frame.pack();
    frame.setVisible(true);
  }

  public static void main(String[] args) {
    // Schedule a job for the event-dispatching thread:
    // creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        createAndShowGUI();
      }
    });
  }
}

A Java JTable example, with AbstractTableModel, JScrollPane, isCellEditable, getColumnName, getValueAt

The following Java source code comes from Sun Microsystems, and shows a JTable example, including the use of an AbstractTableModel, a JScrollPane, and methods like:

  • isCellEditable
  • getColumnName
  • getValueAt
  • getRowCount
  • setPreferredScrollableViewportSize

Here’s the example Java JTable source code:

/**
 * Copyright (c) 2006 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * -Redistribution of source code must retain the above copyright notice, this
 *  list of conditions and the following disclaimer.
 *
 * -Redistribution in binary form must reproduce the above copyright notice,
 *  this list of conditions and the following disclaimer in the documentation
 *  and/or other materials provided with the distribution.
 *
 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MIDROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
 * AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
 * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST
 * REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL,
 * INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY
 * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE,
 * EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 *
 * You acknowledge that this software is not designed, licensed or intended
 * for use in the design, construction, operation or maintenance of any
 * nuclear facility.
 */

/**
 * TableDemo.java is a 1.4 application that requires no other files.
 */

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.table.AbstractTableModel;
import java.awt.Dimension;
import java.awt.GridLayout;

/**
 * TableDemo is just like SimpleTableDemo, except that it uses a custom
 * TableModel.
 */
public class TableDemo extends JPanel {
  private boolean DEBUG = false;

  public TableDemo() {
    super(new GridLayout(1, 0));

    JTable table = new JTable(new MyTableModel());
    table.setPreferredScrollableViewportSize(new Dimension(500, 70));

    //Create the scroll pane and add the table to it.
    JScrollPane scrollPane = new JScrollPane(table);

    //Add the scroll pane to this panel.
    add(scrollPane);
  }

  class MyTableModel extends AbstractTableModel {
    private String[] columnNames = { "First Name", "Last Name", "Sport",
        "# of Years", "Vegetarian" };

    private Object[][] data = {
        { "Mary", "Campione", "Snowboarding", new Integer(5),
            new Boolean(false) },
        { "Alison", "Huml", "Rowing", new Integer(3), new Boolean(true) },
        { "Kathy", "Walrath", "Knitting", new Integer(2),
            new Boolean(false) },
        { "Sharon", "Zakhour", "Speed reading", new Integer(20),
            new Boolean(true) },
        { "Philip", "Milne", "Pool", new Integer(10),
            new Boolean(false) } };

    public int getColumnCount() {
      return columnNames.length;
    }

    public int getRowCount() {
      return data.length;
    }

    public String getColumnName(int col) {
      return columnNames[col];
    }

    public Object getValueAt(int row, int col) {
      return data[row][col];
    }

    /**
     * JTable uses this method to determine the default renderer/ editor for
     * each cell. If we didn't implement this method, then the last column
     * would contain text ("true"/"false"), rather than a check box.
     */
    public Class getColumnClass(int c) {
      return getValueAt(0, c).getClass();
    }

    /**
     * Don't need to implement this method unless your table's editable.
     */
    public boolean isCellEditable(int row, int col) {
      //Note that the data/cell address is constant,
      //no matter where the cell appears onscreen.
      if (col < 2) {
        return false;
      } else {
        return true;
      }
    }

    /**
     * Don't need to implement this method unless your table's data can
     * change.
     */
    public void setValueAt(Object value, int row, int col) {
      if (DEBUG) {
        System.out.println("Setting value at " + row + "," + col
            + " to " + value + " (an instance of "
            + value.getClass() + ")");
      }

      data[row][col] = value;
      fireTableCellUpdated(row, col);

      if (DEBUG) {
        System.out.println("New value of data:");
        printDebugData();
      }
    }

    private void printDebugData() {
      int numRows = getRowCount();
      int numCols = getColumnCount();

      for (int i = 0; i < numRows; i++) {
        System.out.print("    row " + i + ":");
        for (int j = 0; j < numCols; j++) {
          System.out.print("  " + data[i][j]);
        }
        System.out.println();
      }
      System.out.println("--------------------------");
    }
  }

  /**
   * Create the GUI and show it. For thread safety, this method should be
   * invoked from the event-dispatching thread.
   */
  private static void createAndShowGUI() {
    //Make sure we have nice window decorations.
    JFrame.setDefaultLookAndFeelDecorated(true);

    //Create and set up the window.
    JFrame frame = new JFrame("TableDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //Create and set up the content pane.
    TableDemo newContentPane = new TableDemo();
    newContentPane.setOpaque(true); //content panes must be opaque
    frame.setContentPane(newContentPane);

    //Display the window.
    frame.pack();
    frame.setVisible(true);
  }

  public static void main(String[] args) {
    //Schedule a job for the event-dispatching thread:
    //creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        createAndShowGUI();
      }
    });
  }
}

A Java JComboBox example with ActionListener, addActionListener, actionPerformed, getSelectedItem

The following source code comes from Sun Microsystems, and shows a JComboBox, ActionListener, and methods like addActionListener, actionPerformed, getSelectedItem, and more.

Here’s the example Java source code:

/**
 * Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Sun Microsystems nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.SimpleDateFormat;
import java.util.Date;

import javax.swing.BorderFactory;
import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.JComboBox;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

/** ComboBoxDemo2.java requires no other files. */
public class ComboBoxDemo2 extends JPanel implements ActionListener {
  static JFrame frame;
  JLabel result;
  String currentPattern;

  public ComboBoxDemo2() {
    setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));
    String[] patternExamples = { "dd MMMMM yyyy", "dd.MM.yy", "MM/dd/yy",
        "yyyy.MM.dd G 'at' hh:mm:ss z", "EEE, MMM d, ''yy", "h:mm a",
        "H:mm:ss:SSS", "K:mm a,z", "yyyy.MMMMM.dd GGG hh:mm aaa" };

    currentPattern = patternExamples[0];

    // Set up the UI for selecting a pattern.
    JLabel patternLabel1 = new JLabel("Enter the pattern string or");
    JLabel patternLabel2 = new JLabel("select one from the list:");

    JComboBox patternList = new JComboBox(patternExamples);
    patternList.setEditable(true);
    patternList.addActionListener(this);

    // Create the UI for displaying result.
    JLabel resultLabel = new JLabel("Current Date/Time", JLabel.LEADING); // ==
                                                                          // LEFT
    result = new JLabel(" ");
    result.setForeground(Color.black);
    result.setBorder(BorderFactory.createCompoundBorder(BorderFactory
        .createLineBorder(Color.black), BorderFactory.createEmptyBorder(5, 5,
        5, 5)));

    // Lay out everything.
    JPanel patternPanel = new JPanel();
    patternPanel.setLayout(new BoxLayout(patternPanel, BoxLayout.PAGE_AXIS));
    patternPanel.add(patternLabel1);
    patternPanel.add(patternLabel2);
    patternList.setAlignmentX(Component.LEFT_ALIGNMENT);
    patternPanel.add(patternList);

    JPanel resultPanel = new JPanel(new GridLayout(0, 1));
    resultPanel.add(resultLabel);
    resultPanel.add(result);

    patternPanel.setAlignmentX(Component.LEFT_ALIGNMENT);
    resultPanel.setAlignmentX(Component.LEFT_ALIGNMENT);

    add(patternPanel);
    add(Box.createRigidArea(new Dimension(0, 10)));
    add(resultPanel);

    setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));

    reformat();
  } // constructor

  public void actionPerformed(ActionEvent e) {
    JComboBox cb = (JComboBox) e.getSource();
    String newSelection = (String) cb.getSelectedItem();
    currentPattern = newSelection;
    reformat();
  }

  /** Formats and displays today's date. */
  public void reformat() {
    Date today = new Date();
    SimpleDateFormat formatter = new SimpleDateFormat(currentPattern);
    try {
      String dateString = formatter.format(today);
      result.setForeground(Color.black);
      result.setText(dateString);
    } catch (IllegalArgumentException iae) {
      result.setForeground(Color.red);
      result.setText("Error: " + iae.getMessage());
    }
  }

  /**
   * Create the GUI and show it. For thread safety, this method should be
   * invoked from the event-dispatching thread.
   */
  private static void createAndShowGUI() {
    // Create and set up the window.
    JFrame frame = new JFrame("ComboBoxDemo2");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    // Create and set up the content pane.
    JComponent newContentPane = new ComboBoxDemo2();
    newContentPane.setOpaque(true); // content panes must be opaque
    frame.setContentPane(newContentPane);

    // Display the window.
    frame.pack();
    frame.setVisible(true);
  }

  public static void main(String[] args) {
    // Schedule a job for the event-dispatching thread:
    // creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        createAndShowGUI();
      }
    });
  }
}

A Java MouseListener example, with addMouseListener, mousePressed, mouseReleased, mouseEntered, mouseExited, mouseClicked, and MouseEvent

The following source code comes from Sun Microsystems, and shows how to implement a MouseListener, including the following MouseListener methods, which all take a MouseEvent:

  • addMouseListener
  • mousePressed
  • mouseReleased
  • mouseEntered
  • mouseExited
  • mouseClicked

Here’s the example Java source code:

/**
 * Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Sun Microsystems nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * MouseEventDemo.java
 */

import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

import javax.swing.BorderFactory;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class MouseEventDemo extends JPanel implements MouseListener {
  BlankArea blankArea;
  JTextArea textArea;
  static final String NEWLINE = System.getProperty("line.separator");

  public static void main(String[] args) {
    /** Use an appropriate Look and Feel */
    try {
      // UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
      // UIManager.setLookAndFeel("com.sun.java.swing.plaf.gtk.GTKLookAndFeel");
      UIManager.setLookAndFeel("javax.swing.plaf.metal.MetalLookAndFeel");
    } catch (UnsupportedLookAndFeelException ex) {
      ex.printStackTrace();
    } catch (IllegalAccessException ex) {
      ex.printStackTrace();
    } catch (InstantiationException ex) {
      ex.printStackTrace();
    } catch (ClassNotFoundException ex) {
      ex.printStackTrace();
    }
    /** Turn off metal's use of bold fonts */
    UIManager.put("swing.boldMetal", Boolean.FALSE);
    // Schedule a job for the event dispatch thread:
    // creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        createAndShowGUI();
      }
    });
  }

  /**
   * Create the GUI and show it. For thread safety, this method should be
   * invoked from the event dispatch thread.
   */
  private static void createAndShowGUI() {
    // Create and set up the window.
    JFrame frame = new JFrame("MouseEventDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    // Create and set up the content pane.
    JComponent newContentPane = new MouseEventDemo();
    newContentPane.setOpaque(true); // content panes must be opaque
    frame.setContentPane(newContentPane);

    // Display the window.
    frame.pack();
    frame.setVisible(true);
  }

  public MouseEventDemo() {
    super(new GridLayout(0, 1));
    blankArea = new BlankArea(Color.YELLOW);
    add(blankArea);
    textArea = new JTextArea();
    textArea.setEditable(false);
    JScrollPane scrollPane = new JScrollPane(textArea);
    scrollPane
        .setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
    scrollPane.setPreferredSize(new Dimension(200, 75));
    add(scrollPane);

    // Register for mouse events on blankArea and the panel.
    blankArea.addMouseListener(this);
    addMouseListener(this);
    setPreferredSize(new Dimension(450, 450));
    setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
  }

  void eventOutput(String eventDescription, MouseEvent e) {
    textArea.append(eventDescription + " detected on "
        + e.getComponent().getClass().getName() + "." + NEWLINE);
    textArea.setCaretPosition(textArea.getDocument().getLength());
  }

  public void mousePressed(MouseEvent e) {
    eventOutput("Mouse pressed (# of clicks: " + e.getClickCount() + ")", e);
  }

  public void mouseReleased(MouseEvent e) {
    eventOutput("Mouse released (# of clicks: " + e.getClickCount() + ")", e);
  }

  public void mouseEntered(MouseEvent e) {
    eventOutput("Mouse entered", e);
  }

  public void mouseExited(MouseEvent e) {
    eventOutput("Mouse exited", e);
  }

  public void mouseClicked(MouseEvent e) {
    eventOutput("Mouse clicked (# of clicks: " + e.getClickCount() + ")", e);
  }
}

A Java JButton example, showing ImageIcon, actionPerformed, setEnabled, setMnemonic, and setToolTipText

The following source code example comes from Sun Microsystems, and shows various things related to showing and clicking a JButton, including using the JButton class, ActionListener, ActionEvent, ImageIcon, setEnabled, setMnemonic, setToolTipText, and actionPerformed.

jbutton, actionperformed, actionlistener, actionevent, setmnemonic, java, swing, jframe, jpanel, tool tip, tooltip, image, imageicon, event, click

/**
 * Copyright (c) 2006 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * -Redistribution of source code must retain the above copyright notice, this
 *  list of conditions and the following disclaimer.
 *
 * -Redistribution in binary form must reproduce the above copyright notice,
 *  this list of conditions and the following disclaimer in the documentation
 *  and/or other materials provided with the distribution.
 *
 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MIDROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
 * AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
 * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST
 * REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL,
 * INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY
 * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE,
 * EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 *
 * You acknowledge that this software is not designed, licensed or intended
 * for use in the design, construction, operation or maintenance of any
 * nuclear facility.
 */

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;

import javax.swing.AbstractButton;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

/**
 * SwingButtonDemo.java is a 1.4 application that requires the following files:
 * images/right.gif images/middle.gif images/left.gif
 */
public class SwingButtonDemo extends JPanel implements ActionListener {
  protected JButton b1, b2, b3;

  public SwingButtonDemo() {
    ImageIcon leftButtonIcon = createImageIcon("images/right.gif");
    ImageIcon middleButtonIcon = createImageIcon("images/middle.gif");
    ImageIcon rightButtonIcon = createImageIcon("images/left.gif");

    b1 = new JButton("Disable middle button", leftButtonIcon);
    b1.setVerticalTextPosition(AbstractButton.CENTER);
    b1.setHorizontalTextPosition(AbstractButton.LEADING); //aka LEFT, for
    // left-to-right
    // locales
    b1.setMnemonic(KeyEvent.VK_D);
    b1.setActionCommand("disable");

    b2 = new JButton("Middle button", middleButtonIcon);
    b2.setVerticalTextPosition(AbstractButton.BOTTOM);
    b2.setHorizontalTextPosition(AbstractButton.CENTER);
    b2.setMnemonic(KeyEvent.VK_M);

    b3 = new JButton("Enable middle button", rightButtonIcon);
    //Use the default text position of CENTER, TRAILING (RIGHT).
    b3.setMnemonic(KeyEvent.VK_E);
    b3.setActionCommand("enable");
    b3.setEnabled(false);

    //Listen for actions on buttons 1 and 3.
    b1.addActionListener(this);
    b3.addActionListener(this);

    b1.setToolTipText("Click this button to disable the middle button.");
    b2.setToolTipText("This middle button does nothing when you click it.");
    b3.setToolTipText("Click this button to enable the middle button.");

    //Add Components to this container, using the default FlowLayout.
    add(b1);
    add(b2);
    add(b3);
  }

  public void actionPerformed(ActionEvent e) {
    if ("disable".equals(e.getActionCommand())) {
      b2.setEnabled(false);
      b1.setEnabled(false);
      b3.setEnabled(true);
    } else {
      b2.setEnabled(true);
      b1.setEnabled(true);
      b3.setEnabled(false);
    }
  }

  /** Returns an ImageIcon, or null if the path was invalid. */
  protected static ImageIcon createImageIcon(String path) {
    java.net.URL imgURL = SwingButtonDemo.class.getResource(path);
    if (imgURL != null) {
      return new ImageIcon(imgURL);
    } else {
      System.err.println("Couldn't find file: " + path);
      return null;
    }
  }

  /**
   * Create the GUI and show it. For thread safety, this method should be
   * invoked from the event-dispatching thread.
   */
  private static void createAndShowGUI() {
    //Make sure we have nice window decorations.
    JFrame.setDefaultLookAndFeelDecorated(true);

    //Create and set up the window.
    JFrame frame = new JFrame("SwingButtonDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //Create and set up the content pane.
    SwingButtonDemo newContentPane = new SwingButtonDemo();
    newContentPane.setOpaque(true); //content panes must be opaque
    frame.setContentPane(newContentPane);

    //Display the window.
    frame.pack();
    frame.setVisible(true);
  }

  public static void main(String[] args) {
    //Schedule a job for the event-dispatching thread:
    //creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        createAndShowGUI();
      }
    });
  }
}

A JButton example showing ActionListener, ActionEvent, setMnemonic, and actionPerformed

The following source code comes from Sun Microsystems, and shows various things related to showing and clicking a JButton, including using the JButton class, ActionListener, ActionEvent, setMnemonic, and actionPerformed.

jbutton, actionperformed, actionlistener, actionevent, setmnemonic, java, swing, jframe, jpanel

/**
 * Copyright (c) 2006 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * -Redistribution of source code must retain the above copyright notice, this
 *  list of conditions and the following disclaimer.
 *
 * -Redistribution in binary form must reproduce the above copyright notice,
 *  this list of conditions and the following disclaimer in the documentation
 *  and/or other materials provided with the distribution.
 *
 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MIDROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
 * AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
 * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST
 * REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL,
 * INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY
 * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE,
 * EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 *
 * You acknowledge that this software is not designed, licensed or intended
 * for use in the design, construction, operation or maintenance of any
 * nuclear facility.
 */

// v 1.3

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;

import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.UIManager;

public class SwingApplication {
  private static String labelPrefix = "Number of button clicks: ";

  private int numClicks = 0;

  public Component createComponents() {
    final JLabel label = new JLabel(labelPrefix + "0    ");

    JButton button = new JButton("I'm a Swing button!");
    button.setMnemonic(KeyEvent.VK_I);
    button.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        numClicks++;
        label.setText(labelPrefix + numClicks);
      }
    });
    label.setLabelFor(button);

    /**
     * An easy way to put space between a top-level container and its
     * contents is to put the contents in a JPanel that has an "empty"
     * border.
     */
    JPanel pane = new JPanel();
    pane.setBorder(BorderFactory.createEmptyBorder(30, //top
        30, //left
        10, //bottom
        30) //right
        );
    pane.setLayout(new GridLayout(0, 1));
    pane.add(button);
    pane.add(label);

    return pane;
  }

  public static void main(String[] args) {
    try {
      UIManager.setLookAndFeel(UIManager
          .getCrossPlatformLookAndFeelClassName());
    } catch (Exception e) {
    }

    //Create the top-level container and add contents to it.
    JFrame frame = new JFrame("SwingApplication");
    SwingApplication app = new SwingApplication();
    Component contents = app.createComponents();
    frame.getContentPane().add(contents, BorderLayout.CENTER);

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setVisible(true);
  }
}

A Java MouseEvent, MouseMotionListener example with mouseMoved and mouseDragged

The following source code comes from Sun Microsystems, and shows various things related to handling mouse events, including MouseEvent, MouseMotionListener, and the mouseDragged and mouseMoved methods that accept MouseEvent objects.

/**
 * Copyright (c) 2006 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * -Redistribution of source code must retain the above copyright notice, this
 *  list of conditions and the following disclaimer.
 *
 * -Redistribution in binary form must reproduce the above copyright notice,
 *  this list of conditions and the following disclaimer in the documentation
 *  and/or other materials provided with the distribution.
 *
 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MIDROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
 * AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
 * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST
 * REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL,
 * INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY
 * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE,
 * EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 *
 * You acknowledge that this software is not designed, licensed or intended
 * for use in the design, construction, operation or maintenance of any
 * nuclear facility.
 */

/**
 * SwingMouseMotionEventDemo.java is a 1.2/1.3/1.4 example that requires the
 * following file: BlankArea.java
 */

import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;

import javax.swing.BorderFactory;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;

public class SwingMouseMotionEventDemo extends JPanel implements MouseMotionListener {
  BlankArea blankArea;

  JTextArea textArea;

  static final String newline = "\n";

  public SwingMouseMotionEventDemo() {
    super(new GridBagLayout());
    GridBagLayout gridbag = (GridBagLayout) getLayout();
    GridBagConstraints c = new GridBagConstraints();

    c.fill = GridBagConstraints.BOTH;
    c.gridwidth = GridBagConstraints.REMAINDER;
    c.weightx = 1.0;
    c.weighty = 1.0;

    c.insets = new Insets(1, 1, 1, 1);
    blankArea = new BlankArea(new Color(0.98f, 0.97f, 0.85f));
    gridbag.setConstraints(blankArea, c);
    add(blankArea);

    c.insets = new Insets(0, 0, 0, 0);
    textArea = new JTextArea();
    textArea.setEditable(false);
    JScrollPane scrollPane = new JScrollPane(textArea,
        JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
        JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
    scrollPane.setPreferredSize(new Dimension(200, 75));
    gridbag.setConstraints(scrollPane, c);
    add(scrollPane);

    //Register for mouse events on blankArea and panel.
    blankArea.addMouseMotionListener(this);
    addMouseMotionListener(this);

    setPreferredSize(new Dimension(450, 450));
    setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
  }

  public void mouseMoved(MouseEvent e) {
    saySomething("Mouse moved", e);
  }

  public void mouseDragged(MouseEvent e) {
    saySomething("Mouse dragged", e);
  }

  void saySomething(String eventDescription, MouseEvent e) {
    textArea.append(eventDescription + " (" + e.getX() + "," + e.getY()
        + ")" + " detected on " + e.getComponent().getClass().getName()
        + newline);
    textArea.setCaretPosition(textArea.getDocument().getLength());
  }

  /**
   * Create the GUI and show it. For thread safety, this method should be
   * invoked from the event-dispatching thread.
   */
  private static void createAndShowGUI() {
    //Make sure we have nice window decorations.
    JFrame.setDefaultLookAndFeelDecorated(true);

    //Create and set up the window.
    JFrame frame = new JFrame("SwingMouseMotionEventDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //Create and set up the content pane.
    JComponent newContentPane = new SwingMouseMotionEventDemo();
    newContentPane.setOpaque(true); //content panes must be opaque
    frame.setContentPane(newContentPane);

    //Display the window.
    frame.pack();
    frame.setVisible(true);
  }

  public static void main(String[] args) {
    //Schedule a job for the event-dispatching thread:
    //creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        createAndShowGUI();
      }
    });
  }
}

class BlankArea extends JLabel {
  Dimension minSize = new Dimension(100, 100);

  public BlankArea(Color color) {
    setBackground(color);
    setOpaque(true);
    setBorder(BorderFactory.createLineBorder(Color.black));
  }

  public Dimension getMinimumSize() {
    return minSize;
  }

  public Dimension getPreferredSize() {
    return minSize;
  }
}

A Java JFileChooser example, with ActionEvent, ActionListener, Insets, actionPerformed, showOpenDialog

This is a Java JFileChooser example from Sun Microsystems that shows how to work with a JFileChooser, and also shows related features, including ActionEvent, ActionListener, the actionPerformed and showOpenDialog methods, and more.

(I’ve included it here because I work with Java Swing applications quite a bit, and I want it to be easier to find on my website.)

/**
 * Copyright (c) 2006 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * -Redistribution of source code must retain the above copyright notice, this
 *  list of conditions and the following disclaimer.
 *
 * -Redistribution in binary form must reproduce the above copyright notice,
 *  this list of conditions and the following disclaimer in the documentation
 *  and/or other materials provided with the distribution.
 *
 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MIDROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
 * AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
 * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST
 * REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL,
 * INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY
 * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE,
 * EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 *
 * You acknowledge that this software is not designed, licensed or intended
 * for use in the design, construction, operation or maintenance of any
 * nuclear facility.
 */

import java.awt.BorderLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;

import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JDialog;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;

/**
 * SwingFileChooserDemo.java is a 1.4 application that uses these files:
 * images/Open16.gif images/Save16.gif
 */
public class SwingFileChooserDemo extends JPanel implements ActionListener {
  static private final String newline = "\n";

  JButton openButton, saveButton;

  JTextArea log;

  JFileChooser fc;

  public SwingFileChooserDemo() {
    super(new BorderLayout());

    //Create the log first, because the action listeners
    //need to refer to it.
    log = new JTextArea(5, 20);
    log.setMargin(new Insets(5, 5, 5, 5));
    log.setEditable(false);
    JScrollPane logScrollPane = new JScrollPane(log);

    //Create a file chooser
    fc = new JFileChooser();

    //Uncomment one of the following lines to try a different
    //file selection mode. The first allows just directories
    //to be selected (and, at least in the Java look and feel,
    //shown). The second allows both files and directories
    //to be selected. If you leave these lines commented out,
    //then the default mode (FILES_ONLY) will be used.
    //
    //fc.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
    //fc.setFileSelectionMode(JFileChooser.FILES_AND_DIRECTORIES);

    //Create the open button. We use the image from the JLF
    //Graphics Repository (but we extracted it from the jar).
    openButton = new JButton("Open a File...",
        createImageIcon("images/Open16.gif"));
    openButton.addActionListener(this);

    //Create the save button. We use the image from the JLF
    //Graphics Repository (but we extracted it from the jar).
    saveButton = new JButton("Save a File...",
        createImageIcon("images/Save16.gif"));
    saveButton.addActionListener(this);

    //For layout purposes, put the buttons in a separate panel
    JPanel buttonPanel = new JPanel(); //use FlowLayout
    buttonPanel.add(openButton);
    buttonPanel.add(saveButton);

    //Add the buttons and the log to this panel.
    add(buttonPanel, BorderLayout.PAGE_START);
    add(logScrollPane, BorderLayout.CENTER);
  }

  public void actionPerformed(ActionEvent e) {

    //Handle open button action.
    if (e.getSource() == openButton) {
      int returnVal = fc.showOpenDialog(SwingFileChooserDemo.this);

      if (returnVal == JFileChooser.APPROVE_OPTION) {
        File file = fc.getSelectedFile();
        //This is where a real application would open the file.
        log.append("Opening: " + file.getName() + "." + newline);
      } else {
        log.append("Open command cancelled by user." + newline);
      }
      log.setCaretPosition(log.getDocument().getLength());

      //Handle save button action.
    } else if (e.getSource() == saveButton) {
      int returnVal = fc.showSaveDialog(SwingFileChooserDemo.this);
      if (returnVal == JFileChooser.APPROVE_OPTION) {
        File file = fc.getSelectedFile();
        //This is where a real application would save the file.
        log.append("Saving: " + file.getName() + "." + newline);
      } else {
        log.append("Save command cancelled by user." + newline);
      }
      log.setCaretPosition(log.getDocument().getLength());
    }
  }

  /** Returns an ImageIcon, or null if the path was invalid. */
  protected static ImageIcon createImageIcon(String path) {
    java.net.URL imgURL = SwingFileChooserDemo.class.getResource(path);
    if (imgURL != null) {
      return new ImageIcon(imgURL);
    } else {
      System.err.println("Couldn't find file: " + path);
      return null;
    }
  }

  /**
   * Create the GUI and show it. For thread safety, this method should be
   * invoked from the event-dispatching thread.
   */
  private static void createAndShowGUI() {
    //Make sure we have nice window decorations.
    JFrame.setDefaultLookAndFeelDecorated(true);
    JDialog.setDefaultLookAndFeelDecorated(true);

    //Create and set up the window.
    JFrame frame = new JFrame("SwingFileChooserDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //Create and set up the content pane.
    JComponent newContentPane = new SwingFileChooserDemo();
    newContentPane.setOpaque(true); //content panes must be opaque
    frame.setContentPane(newContentPane);

    //Display the window.
    frame.pack();
    frame.setVisible(true);
  }

  public static void main(String[] args) {
    //Schedule a job for the event-dispatching thread:
    //creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        createAndShowGUI();
      }
    });
  }
}

A Java JList example: DefaultListModel, ListSelectionModel, ListSelectionListener, and ActionListener

This is a Java JList example from Sun Microsystems that shows how to work with a JList, including some of the most common and important features, including DefaultListModel, ListSelectionModel, ListSelectionListener, ActionListener, and more. I’ve included it here because I work with Java Swing applications quite a bit, and I want it to be easier to find on my website.

/**
 * Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Sun Microsystems nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

import java.awt.BorderLayout;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.BorderFactory;
import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.DefaultListModel;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSeparator;
import javax.swing.JTextField;
import javax.swing.ListSelectionModel;
import javax.swing.SwingConstants;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;

// ListDemo.java requires no other files.
public class ListDemo extends JPanel implements ListSelectionListener {
  private JList list;
  private DefaultListModel listModel;

  private static final String hireString = "Hire";
  private static final String fireString = "Fire";
  private JButton fireButton;
  private JTextField employeeName;

  public ListDemo() {
    super(new BorderLayout());

    listModel = new DefaultListModel();
    listModel.addElement("Debbie Scott");
    listModel.addElement("Scott Hommel");
    listModel.addElement("Sharon Zakhour");

    // 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);

    JButton hireButton = new JButton(hireString);
    HireListener hireListener = new HireListener(hireButton);
    hireButton.setActionCommand(hireString);
    hireButton.addActionListener(hireListener);
    hireButton.setEnabled(false);

    fireButton = new JButton(fireString);
    fireButton.setActionCommand(fireString);
    fireButton.addActionListener(new FireListener());

    employeeName = new JTextField(10);
    employeeName.addActionListener(hireListener);
    employeeName.getDocument().addDocumentListener(hireListener);
    String name = listModel.getElementAt(list.getSelectedIndex()).toString();

    // Create a panel that uses BoxLayout.
    JPanel buttonPane = new JPanel();
    buttonPane.setLayout(new BoxLayout(buttonPane, BoxLayout.LINE_AXIS));
    buttonPane.add(fireButton);
    buttonPane.add(Box.createHorizontalStrut(5));
    buttonPane.add(new JSeparator(SwingConstants.VERTICAL));
    buttonPane.add(Box.createHorizontalStrut(5));
    buttonPane.add(employeeName);
    buttonPane.add(hireButton);
    buttonPane.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));

    add(listScrollPane, BorderLayout.CENTER);
    add(buttonPane, BorderLayout.PAGE_END);
  }

  class FireListener implements ActionListener {
    public void actionPerformed(ActionEvent e) {
      // This method can be called only if
      // there's a valid selection
      // so go ahead and remove whatever's selected.
      int index = list.getSelectedIndex();
      listModel.remove(index);

      int size = listModel.getSize();

      if (size == 0) { // Nobody's left, disable firing.
        fireButton.setEnabled(false);

      } else { // Select an index.
        if (index == listModel.getSize()) {
          // removed item in last position
          index--;
        }

        list.setSelectedIndex(index);
        list.ensureIndexIsVisible(index);
      }
    }
  }

  // This listener is shared by the text field and the hire button.
  class HireListener implements ActionListener, DocumentListener {
    private boolean alreadyEnabled = false;
    private JButton button;

    public HireListener(JButton button) {
      this.button = button;
    }

    // Required by ActionListener.
    public void actionPerformed(ActionEvent e) {
      String name = employeeName.getText();

      // User didn't type in a unique name...
      if (name.equals("") || alreadyInList(name)) {
        Toolkit.getDefaultToolkit().beep();
        employeeName.requestFocusInWindow();
        employeeName.selectAll();
        return;
      }

      int index = list.getSelectedIndex(); // get selected index
      if (index == -1) { // no selection, so insert at beginning
        index = 0;
      } else { // add after the selected item
        index++;
      }

      listModel.insertElementAt(employeeName.getText(), index);
      // If we just wanted to add to the end, we'd do this:
      // listModel.addElement(employeeName.getText());

      // Reset the text field.
      employeeName.requestFocusInWindow();
      employeeName.setText("");

      // Select the new item and make it visible.
      list.setSelectedIndex(index);
      list.ensureIndexIsVisible(index);
    }

    // This method tests for string equality. You could certainly
    // get more sophisticated about the algorithm. For example,
    // you might want to ignore white space and capitalization.
    protected boolean alreadyInList(String name) {
      return listModel.contains(name);
    }

    // Required by DocumentListener.
    public void insertUpdate(DocumentEvent e) {
      enableButton();
    }

    // Required by DocumentListener.
    public void removeUpdate(DocumentEvent e) {
      handleEmptyTextField(e);
    }

    // Required by DocumentListener.
    public void changedUpdate(DocumentEvent e) {
      if (!handleEmptyTextField(e)) {
        enableButton();
      }
    }

    private void enableButton() {
      if (!alreadyEnabled) {
        button.setEnabled(true);
      }
    }

    private boolean handleEmptyTextField(DocumentEvent e) {
      if (e.getDocument().getLength() <= 0) {
        button.setEnabled(false);
        alreadyEnabled = false;
        return true;
      }
      return false;
    }
  }

  // This method is required by ListSelectionListener.
  public void valueChanged(ListSelectionEvent e) {
    if (e.getValueIsAdjusting() == false) {

      if (list.getSelectedIndex() == -1) {
        // No selection, disable fire button.
        fireButton.setEnabled(false);

      } else {
        // Selection, enable the fire button.
        fireButton.setEnabled(true);
      }
    }
  }

  /**
   * Create the GUI and show it. For thread safety, this method should be
   * invoked from the event-dispatching thread.
   */
  private static void createAndShowGUI() {
    // Create and set up the window.
    JFrame frame = new JFrame("ListDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    // Create and set up the content pane.
    JComponent newContentPane = new ListDemo();
    newContentPane.setOpaque(true); // content panes must be opaque
    frame.setContentPane(newContentPane);

    // Display the window.
    frame.pack();
    frame.setVisible(true);
  }

  public static void main(String[] args) {
    // Schedule a job for the event-dispatching thread:
    // creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        createAndShowGUI();
      }
    });
  }
}