Java/Swing JFC/Focus

Button Focus

  
import java.awt.Container;
import java.awt.FlowLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
public class ButtonFocus {
  public static void main(String args[]) {
    JFrame frame = new JFrame("Action Sample");
    JButton focusButton = new JButton("Focused");
    JButton notFocusButton = new JButton("Not Focused");
    Container contentPane = frame.getContentPane();
    contentPane.setLayout(new FlowLayout());
    contentPane.add(focusButton);
    contentPane.add(notFocusButton);
    frame.setSize(300, 100);
    frame.setVisible(true);
  }
}

Focus Concepts Demo

  
/* From http://java.sun.ru/docs/books/tutorial/index.html */
/*
 * 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.GridLayout;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.JTextField;
/*
 * FocusConceptsDemo.java is a 1.4 example that requires no other files.
 */
public class FocusConceptsDemo extends JPanel {
  static JFrame frame;
  JTextField t1, t2, t3, t4;
  JButton b1, b2, b3, b4;
  JTextArea text1;
  public FocusConceptsDemo() {
    super(new BorderLayout());
    b1 = new JButton("JButton");
    b2 = new JButton("JButton");
    b3 = new JButton("JButton");
    b4 = new JButton("JButton");
    JPanel buttonPanel = new JPanel(new GridLayout(1, 1));
    buttonPanel.add(b1);
    buttonPanel.add(b2);
    buttonPanel.add(b3);
    buttonPanel.add(b4);
    text1 = new JTextArea("JTextArea", 15, 40);
    JPanel textAreaPanel = new JPanel(new BorderLayout());
    textAreaPanel.add(text1, BorderLayout.CENTER);
    t1 = new JTextField("JTextField");
    t2 = new JTextField("JTextField");
    t3 = new JTextField("JTextField");
    t4 = new JTextField("JTextField");
    JPanel textFieldPanel = new JPanel(new GridLayout(1, 1));
    textFieldPanel.add(t1);
    textFieldPanel.add(t2);
    textFieldPanel.add(t3);
    textFieldPanel.add(t4);
    add(buttonPanel, BorderLayout.PAGE_START);
    add(textAreaPanel, BorderLayout.CENTER);
    add(textFieldPanel, BorderLayout.PAGE_END);
    setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
  }
  /**
   * 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.
    frame = new JFrame("FocusConceptsDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    //Create and set up the content pane.
    JComponent newContentPane = new FocusConceptsDemo();
    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();
      }
    });
  }
}

Focus Cycle Sample

  
import java.awt.Container;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class FocusCycleSample {
  public static void main(String args[]) {
    JFrame frame = new JFrame("Focus Cycle Sample");
    Container contentPane = frame.getContentPane();
    contentPane.setLayout(new GridLayout(3,3));
    for (int i = 0; i < 8; i++) {
      JButton button = new JButton("" + i);
      contentPane.add(button);
    }
    JPanel panel = new FocusCycleConstrainedJPanel();
    panel.setLayout(new GridLayout(1, 3));
    for (int i = 0; i < 3; i++) {
      JButton button = new JButton("" + (i + 3));
      panel.add(button);
    }
    contentPane.add(panel);
    frame.setSize(300, 200);
    frame.setVisible(true);
  }
}
class FocusCycleConstrainedJPanel extends JPanel {
  public boolean isFocusCycleRoot() {
    return true;
  }
}

Focus Example

  
import java.awt.AWTKeyStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.KeyboardFocusManager;
import java.awt.event.KeyEvent;
import javax.swing.JButton;
import javax.swing.JDesktopPane;
import javax.swing.JFrame;
import javax.swing.JInternalFrame;
import javax.swing.JPanel;
public class FocusExample extends JFrame {
  public FocusExample() {
    super("Focus Example");
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    MyPanel mypanel = new MyPanel();
    JButton button1 = new JButton("One");
    JButton button2 = new JButton("Two");
    JButton button3 = new JButton("Three");
    JButton button4 = new JButton("Four");
    JButton button5 = new MyButton("Five*");
    JButton button6 = new MyButton("Six*");
    JButton button7 = new JButton("Seven");
    mypanel.add(button2);
    mypanel.add(button3);
    JInternalFrame frame1 = new JInternalFrame("Internal Frame 1", true,
        true, true, true);
    frame1.setBackground(Color.lightGray);
    frame1.getContentPane().setLayout(new GridLayout(2, 3));
    frame1.setSize(300, 200);
    frame1.getContentPane().add(button1);
    frame1.getContentPane().add(mypanel);
    frame1.getContentPane().add(button4);
    frame1.getContentPane().add(button5);
    frame1.getContentPane().add(button6);
    frame1.getContentPane().add(button7);
    JDesktopPane desktop = new JDesktopPane();
    desktop.add(frame1, new Integer(1));
    desktop.setOpaque(true);
    //  Now set up the user interface window.
    Container contentPane = getContentPane();
    contentPane.add(desktop, BorderLayout.CENTER);
    setSize(new Dimension(400, 300));
    frame1.setVisible(true);
    setVisible(true);
  }
  public static void main(String[] args) {
    new FocusExample();
  }
  class MyButton extends JButton {
    public MyButton(String s) {
      super(s);
    }
    public boolean isFocusable() {
      return false;
    }
  }
  class MyPanel extends JPanel {
    public MyPanel() {
      super(true);
      java.util.Set upKeys = new java.util.HashSet(1);
      upKeys.add(AWTKeyStroke.getAWTKeyStroke(KeyEvent.VK_UP, 0));
      setFocusTraversalKeys(KeyboardFocusManager.UP_CYCLE_TRAVERSAL_KEYS,
          upKeys);
    }
    public boolean isFocusCycleRoot() {
      return true;
    }
  }
}

Focus Traversal Demo

  
/* From http://java.sun.ru/docs/books/tutorial/index.html */
/*
 * 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.ruponent;
import java.awt.Container;
import java.awt.FocusTraversalPolicy;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BorderFactory;
import javax.swing.JCheckBox;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTable;
import javax.swing.JTextField;
/*
 * FocusTraversalDemo.java is a 1.4 example that requires no other files.
 */
public class FocusTraversalDemo extends JPanel implements ActionListener {
  static JFrame frame;
  JTextField tf1, tf2, tf3, tf4, tf5, tf6;
  JTable table;
  JLabel label;
  JCheckBox togglePolicy;
  static MyOwnFocusTraversalPolicy newPolicy;
  public FocusTraversalDemo() {
    super(new BorderLayout());
    newPolicy = new MyOwnFocusTraversalPolicy();
    tf1 = new JTextField("Field 1");
    tf2 = new JTextField("A Bigger Field 2");
    tf3 = new JTextField("Field 3");
    tf4 = new JTextField("A Bigger Field 4");
    tf5 = new JTextField("Field 5");
    tf6 = new JTextField("A Bigger Field 6");
    table = new JTable(4, 3);
    togglePolicy = new JCheckBox("Custom FocusTraversalPolicy");
    togglePolicy.setActionCommand("toggle");
    togglePolicy.addActionListener(this);
    togglePolicy.setFocusable(false); //Remove it from the focus cycle.
    //Note that HTML is allowed and will break this run of text
    //across two lines.
    label = new JLabel(
        "<html>Use Tab (or Shift-Tab) to navigate from component to component.<p>Control-Tab (or Control-Shift-Tab) allows you to break out of the JTable.</html>");
    JPanel leftTextPanel = new JPanel(new GridLayout(3, 2));
    leftTextPanel.add(tf1, BorderLayout.PAGE_START);
    leftTextPanel.add(tf3, BorderLayout.CENTER);
    leftTextPanel.add(tf5, BorderLayout.PAGE_END);
    leftTextPanel.setBorder(BorderFactory.createEmptyBorder(0, 0, 5, 5));
    JPanel rightTextPanel = new JPanel(new GridLayout(3, 2));
    rightTextPanel.add(tf2, BorderLayout.PAGE_START);
    rightTextPanel.add(tf4, BorderLayout.CENTER);
    rightTextPanel.add(tf6, BorderLayout.PAGE_END);
    rightTextPanel.setBorder(BorderFactory.createEmptyBorder(0, 0, 5, 5));
    JPanel tablePanel = new JPanel(new GridLayout(0, 1));
    tablePanel.add(table, BorderLayout.CENTER);
    tablePanel.setBorder(BorderFactory.createEtchedBorder());
    JPanel bottomPanel = new JPanel(new GridLayout(2, 1));
    bottomPanel.add(togglePolicy, BorderLayout.PAGE_START);
    bottomPanel.add(label, BorderLayout.PAGE_END);
    add(leftTextPanel, BorderLayout.LINE_START);
    add(rightTextPanel, BorderLayout.CENTER);
    add(tablePanel, BorderLayout.LINE_END);
    add(bottomPanel, BorderLayout.PAGE_END);
    setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
  }
  //Turn the custom focus traversal policy on/off,
  //according to the checkbox
  public void actionPerformed(ActionEvent e) {
    if ("toggle".equals(e.getActionCommand())) {
      frame.setFocusTraversalPolicy(togglePolicy.isSelected() ? newPolicy
          : 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.
    frame = new JFrame("FocusTraversalDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    //Create and set up the content pane.
    JComponent newContentPane = new FocusTraversalDemo();
    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();
      }
    });
  }
  public class MyOwnFocusTraversalPolicy extends FocusTraversalPolicy {
    public Component getComponentAfter(Container focusCycleRoot,
        Component aComponent) {
      if (aComponent.equals(tf1)) {
        return tf2;
      } else if (aComponent.equals(tf2)) {
        return tf3;
      } else if (aComponent.equals(tf3)) {
        return tf4;
      } else if (aComponent.equals(tf4)) {
        return tf5;
      } else if (aComponent.equals(tf5)) {
        return tf6;
      } else if (aComponent.equals(tf6)) {
        return table;
      } else if (aComponent.equals(table)) {
        return tf1;
      }
      return tf1;
    }
    public Component getComponentBefore(Container focusCycleRoot,
        Component aComponent) {
      if (aComponent.equals(tf1)) {
        return table;
      } else if (aComponent.equals(tf2)) {
        return tf1;
      } else if (aComponent.equals(tf3)) {
        return tf2;
      } else if (aComponent.equals(tf4)) {
        return tf3;
      } else if (aComponent.equals(tf5)) {
        return tf4;
      } else if (aComponent.equals(tf6)) {
        return tf5;
      } else if (aComponent.equals(table)) {
        return tf6;
      }
      return tf1;
    }
    public Component getDefaultComponent(Container focusCycleRoot) {
      return tf1;
    }
    public Component getLastComponent(Container focusCycleRoot) {
      return table;
    }
    public Component getFirstComponent(Container focusCycleRoot) {
      return tf1;
    }
  }
}

Focus Traversal Example

  
/*
Java Swing, 2nd Edition
By Marc Loy, Robert Eckstein, Dave Wood, James Elliott, Brian Cole
ISBN: 0-596-00408-7
Publisher: O"Reilly 
*/
// FocusTraversalExample.java
//Similar to the FocusExample, this class uses the custom AlphaButtonPolicy
//focus traversal policy to navigate another small set of buttons.
//
import java.awt.Color;
import java.awt.ruponent;
import java.awt.Container;
import java.awt.FocusTraversalPolicy;
import java.awt.GridLayout;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class FocusTraversalExample extends JPanel {
  public FocusTraversalExample() {
    setLayout(new GridLayout(6, 1));
    JButton button1 = new JButton("Texas");
    JButton button2 = new JButton("Vermont");
    JButton button3 = new JButton("Florida");
    JButton button4 = new JButton("Alabama");
    JButton button5 = new JButton("Minnesota");
    JButton button6 = new JButton("California");
    setBackground(Color.lightGray);
    add(button1);
    add(button2);
    add(button3);
    add(button4);
    add(button5);
    add(button6);
  }
  public static void main(String[] args) {
    JFrame frame = new JFrame("Alphabetized Button Focus Traversal");
    frame.setFocusTraversalPolicy(new AlphaButtonPolicy());
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setContentPane(new FocusTraversalExample());
    frame.setSize(400, 300);
    frame.setVisible(true);
  }
}
//AlphaButtonPolicy.java
//A custom focus traversal policy that uses alphabetical ordering of button
//labels to determine "next" and "previous" buttons for keyboard traversal.
//
class AlphaButtonPolicy extends FocusTraversalPolicy {
  private SortedMap getSortedButtons(Container focusCycleRoot) {
    if (focusCycleRoot == null) {
      throw new IllegalArgumentException("focusCycleRoot can"t be null");
    }
    SortedMap result = new TreeMap(); // Will sort all buttons by text.
    sortRecursive(result, focusCycleRoot);
    return result;
  }
  private void sortRecursive(Map buttons, Container container) {
    for (int i = 0; i < container.getComponentCount(); i++) {
      Component c = container.getComponent(i);
      if (c instanceof JButton) { // Found another button to sort.
        buttons.put(((JButton) c).getText(), c);
      }
      if (c instanceof Container) { // Found a container to search.
        sortRecursive(buttons, (Container) c);
      }
    }
  }
  // The rest of the code implements the FocusTraversalPolicy interface.
  public Component getFirstComponent(Container focusCycleRoot) {
    SortedMap buttons = getSortedButtons(focusCycleRoot);
    if (buttons.isEmpty()) {
      return null;
    }
    return (Component) buttons.get(buttons.firstKey());
  }
  public Component getLastComponent(Container focusCycleRoot) {
    SortedMap buttons = getSortedButtons(focusCycleRoot);
    if (buttons.isEmpty()) {
      return null;
    }
    return (Component) buttons.get(buttons.lastKey());
  }
  public Component getDefaultComponent(Container focusCycleRoot) {
    return getFirstComponent(focusCycleRoot);
  }
  public Component getComponentAfter(Container focusCycleRoot,
      Component aComponent) {
    if (!(aComponent instanceof JButton)) {
      return null;
    }
    SortedMap buttons = getSortedButtons(focusCycleRoot);
    // Find all buttons after the current one.
    String nextName = ((JButton) aComponent).getText() + "\0";
    SortedMap nextButtons = buttons.tailMap(nextName);
    if (nextButtons.isEmpty()) { // Wrapped back to beginning
      if (!buttons.isEmpty()) {
        return (Component) buttons.get(buttons.firstKey());
      }
      return null; // Degenerate case of no buttons.
    }
    return (Component) nextButtons.get(nextButtons.firstKey());
  }
  public Component getComponentBefore(Container focusCycleRoot,
      Component aComponent) {
    if (!(aComponent instanceof JButton)) {
      return null;
    }
    SortedMap buttons = getSortedButtons(focusCycleRoot);
    SortedMap prevButtons = // Find all buttons before this one.
    buttons.headMap(((JButton) aComponent).getText());
    if (prevButtons.isEmpty()) { // Wrapped back to end.
      if (!buttons.isEmpty()) {
        return (Component) buttons.get(buttons.lastKey());
      }
      return null; // Degenerate case of no buttons.
    }
    return (Component) prevButtons.get(prevButtons.lastKey());
  }
}

Handling Focus Changes

   
import java.awt.event.FocusAdapter;
import java.awt.event.FocusEvent;
import javax.swing.JFrame;
import javax.swing.JTextField;
public class Main {
  public static void main(String[] argv) throws Exception {
    JTextField component = new JTextField();
    component.addFocusListener(new MyFocusListener());
    JFrame f = new JFrame();
    f.add(component);
    f.setSize(300, 300);
    f.setVisible(true);
  }
}
class MyFocusListener extends FocusAdapter {
  public void focusGained(FocusEvent evt) {
    System.out.println("component gained the focus");
  }
  public void focusLost(FocusEvent evt) {
    System.out.println("component lost the focus");
  }
}

Requests focus for a component

   
import java.awt.ruponent;
import java.awt.Container;
import java.awt.FocusTraversalPolicy;
import java.awt.KeyboardFocusManager;
import javax.swing.JComponent;
/**
 * Copyright (C) 2004 NNL Technology AB
 * Visit www.infonode.net for information about InfoNode(R) 
 * products and how to contact NNL Technology AB.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, 
 * MA 02111-1307, USA.
 */

// $Id: ComponentUtil.java,v 1.25 2005/12/04 13:46:04 jesper Exp $

public class Util {
  /**
   * Requests focus for a component. If that"s not possible it"s
   * {@link FocusTraversalPolicy}is checked. If that doesn"t work all it"s
   * children is recursively checked with this method.
   *
   * @param component the component to request focus for
   * @return the component which has focus or probably will obtain focus, null
   *         if no component will receive focus
   */
  public static Component smartRequestFocus(Component component) {
    if (requestFocus(component))
      return component;
    if (component instanceof JComponent) {
      FocusTraversalPolicy policy = ((JComponent) component).getFocusTraversalPolicy();
      if (policy != null) {
        Component focusComponent = policy.getDefaultComponent((Container) component);
        if (focusComponent != null && requestFocus(focusComponent)) {
          return focusComponent;
        }
      }
    }
    if (component instanceof Container) {
      Component[] children = ((Container) component).getComponents();
      for (int i = 0; i < children.length; i++) {
        component = smartRequestFocus(children[i]);
        if (component != null)
          return component;
      }
    }
    return null;
  }
  /**
   * Requests focus unless the component already has focus. For some weird
   * reason calling {@link Component#requestFocusInWindow()}when the
   * component is focus owner changes focus owner to another component!
   *
   * @param component the component to request focus for
   * @return true if the component has focus or probably will get focus,
   *         otherwise false
   */
  public static boolean requestFocus(Component component) {
    /*
     * System.out.println("Owner: " +
     * System.identityHashCode(KeyboardFocusManager.getCurrentKeyboardFocusManager().getFocusOwner()) + ", " +
     * System.identityHashCode(component) + ", " +
     * (KeyboardFocusManager.getCurrentKeyboardFocusManager().getFocusOwner() ==
     * component));
     */
    return KeyboardFocusManager.getCurrentKeyboardFocusManager().getFocusOwner() == component ||
           component.requestFocusInWindow();
  }
}

Requests focus unless the component already has focus

   
import java.awt.ruponent;
import java.awt.KeyboardFocusManager;
/**
 * Copyright (C) 2004 NNL Technology AB
 * Visit www.infonode.net for information about InfoNode(R) 
 * products and how to contact NNL Technology AB.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, 
 * MA 02111-1307, USA.
 */

// $Id: ComponentUtil.java,v 1.25 2005/12/04 13:46:04 jesper Exp $

public class Util {
  /**
   * Requests focus unless the component already has focus. For some weird
   * reason calling {@link Component#requestFocusInWindow()}when the
   * component is focus owner changes focus owner to another component!
   *
   * @param component the component to request focus for
   * @return true if the component has focus or probably will get focus,
   *         otherwise false
   */
  public static boolean requestFocus(Component component) {
    /*
     * System.out.println("Owner: " +
     * System.identityHashCode(KeyboardFocusManager.getCurrentKeyboardFocusManager().getFocusOwner()) + ", " +
     * System.identityHashCode(component) + ", " +
     * (KeyboardFocusManager.getCurrentKeyboardFocusManager().getFocusOwner() ==
     * component));
     */
    return KeyboardFocusManager.getCurrentKeyboardFocusManager().getFocusOwner() == component ||
           component.requestFocusInWindow();
  }
}

Track Focus Demo

  
/* From http://java.sun.ru/docs/books/tutorial/index.html */
/*
 * 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.
 */
/*
 * TrackFocusDemo.java is a 1.4 example that requires the following files:
 * Picture.java images/Maya.jpg images/Anya.jpg images/Laine.jpg
 * images/Cosmo.jpg images/Adele.jpg images/Alexi.jpg
 */
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.ruponent;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.Image;
import java.awt.KeyboardFocusManager;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import javax.accessibility.Accessible;
import javax.swing.BorderFactory;
import javax.swing.ImageIcon;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
public class TrackFocusDemo extends JPanel {
  Picture pic1, pic2, pic3, pic4, pic5, pic6;
  JLabel info;
  static String mayaString = "Maya";
  static String anyaString = "Anya";
  static String laineString = "Laine";
  static String cosmoString = "Cosmo";
  static String adeleString = "Adele";
  static String alexiString = "Alexi";
  String[] comments = { "Oops. What is this?", "This is Maya",
      "This is Anya", "This is Laine", "This is Cosmo", "This is Adele",
      "This is Alexi" };
  public TrackFocusDemo() {
    super(new BorderLayout());
    JPanel mugshots = new JPanel(new GridLayout(2, 3));
    pic1 = new Picture(createImageIcon("images/" + mayaString + ".jpg",
        mayaString).getImage());
    pic1.setName("1");
    mugshots.add(pic1);
    pic2 = new Picture(createImageIcon("images/" + anyaString + ".jpg",
        anyaString).getImage());
    pic2.setName("2");
    mugshots.add(pic2);
    pic3 = new Picture(createImageIcon("images/" + laineString + ".jpg",
        laineString).getImage());
    pic3.setName("3");
    mugshots.add(pic3);
    pic4 = new Picture(createImageIcon("images/" + cosmoString + ".jpg",
        cosmoString).getImage());
    pic4.setName("4");
    mugshots.add(pic4);
    pic5 = new Picture(createImageIcon("images/" + adeleString + ".jpg",
        adeleString).getImage());
    pic5.setName("5");
    mugshots.add(pic5);
    pic6 = new Picture(createImageIcon("images/" + alexiString + ".jpg",
        alexiString).getImage());
    pic6.setName("6");
    mugshots.add(pic6);
    info = new JLabel("Nothing selected");
    setPreferredSize(new Dimension(450, 350));
    add(mugshots, BorderLayout.CENTER);
    add(info, BorderLayout.PAGE_END);
    setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
    KeyboardFocusManager focusManager = KeyboardFocusManager
        .getCurrentKeyboardFocusManager();
    focusManager.addPropertyChangeListener(new PropertyChangeListener() {
      public void propertyChange(PropertyChangeEvent e) {
        String prop = e.getPropertyName();
        if (("focusOwner".equals(prop)) && (e.getNewValue() != null)
            && ((e.getNewValue()) instanceof Picture)) {
          Component comp = (Component) e.getNewValue();
          String name = comp.getName();
          Integer num = new Integer(name);
          int index = num.intValue();
          if (index < 0 || index > comments.length) {
            index = 0;
          }
          info.setText(comments[index]);
        }
      }
    });
  }
  /** Returns an ImageIcon, or null if the path was invalid. */
  protected static ImageIcon createImageIcon(String path, String description) {
    java.net.URL imageURL = TrackFocusDemo.class.getResource(path);
    if (imageURL == null) {
      System.err.println("Resource not found: " + path);
      return null;
    } else {
      return new ImageIcon(imageURL, description);
    }
  }
  /**
   * 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("TrackFocusDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JComponent newContentPane = new TrackFocusDemo();
    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();
      }
    });
  }
}
/*
 * Picture.java is used by the 1.4 TrackFocusDemo.java and DragPictureDemo.java
 * examples.
 */
class Picture extends JComponent implements MouseListener, FocusListener,
    Accessible {
  Image image;
  public Picture(Image image) {
    this.image = image;
    setFocusable(true);
    addMouseListener(this);
    addFocusListener(this);
  }
  public void mouseClicked(MouseEvent e) {
    //Since the user clicked on us, let"s get focus!
    requestFocusInWindow();
  }
  public void mouseEntered(MouseEvent e) {
  }
  public void mouseExited(MouseEvent e) {
  }
  public void mousePressed(MouseEvent e) {
  }
  public void mouseReleased(MouseEvent e) {
  }
  public void focusGained(FocusEvent e) {
    //Draw the component with a red border
    //indicating that it has focus.
    this.repaint();
  }
  public void focusLost(FocusEvent e) {
    //Draw the component with a black border
    //indicating that it doesn"t have focus.
    this.repaint();
  }
  protected void paintComponent(Graphics graphics) {
    Graphics g = graphics.create();
    //Draw in our entire space, even if isOpaque is false.
    g.setColor(Color.WHITE);
    g.fillRect(0, 0, image == null ? 125 : image.getWidth(this),
        image == null ? 125 : image.getHeight(this));
    if (image != null) {
      //Draw image at its natural size of 125x125.
      g.drawImage(image, 0, 0, this);
    }
    //Add a border, red if picture currently has focus
    if (isFocusOwner()) {
      g.setColor(Color.RED);
    } else {
      g.setColor(Color.BLACK);
    }
    g.drawRect(0, 0, image == null ? 125 : image.getWidth(this),
        image == null ? 125 : image.getHeight(this));
    g.dispose();
  }
}

Use this method to determine whether a particular component has the focus

  
import javax.swing.JFrame;
public class Main {
  public static void main() {
    JFrame f = new JFrame();
    boolean b = f.isFocusOwner();
  }
}