Java/Event/Focus Event

Changes the focus traversal keys for the entire application.

  

import java.awt.AWTKeyStroke;
import java.awt.KeyboardFocusManager;
import java.util.HashSet;
import java.util.Set;
import javax.swing.KeyStroke;
public class Main {
  public static void main(String[] argv) throws Exception {
    Set<AWTKeyStroke> set = new HashSet<AWTKeyStroke>(KeyboardFocusManager
        .getCurrentKeyboardFocusManager().getDefaultFocusTraversalKeys(
            KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS));
    set.add(KeyStroke.getKeyStroke("F2"));
    KeyboardFocusManager.getCurrentKeyboardFocusManager().setDefaultFocusTraversalKeys(
        KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS, set);
  }
}

Change the backward focus traversal keys for the application

  
import java.awt.AWTKeyStroke;
import java.awt.KeyboardFocusManager;
import java.util.HashSet;
import java.util.Set;
import javax.swing.KeyStroke;
public class Main {
  public static void main(String[] argv) throws Exception {
    Set<AWTKeyStroke> set = new HashSet<AWTKeyStroke>(KeyboardFocusManager
        .getCurrentKeyboardFocusManager().getDefaultFocusTraversalKeys(
            KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS));
    set.add(KeyStroke.getKeyStroke("F3"));
    KeyboardFocusManager.getCurrentKeyboardFocusManager().setDefaultFocusTraversalKeys(
        KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS, set);
  }
}

Change the forward focus traversal keys for a component

  
import java.awt.KeyboardFocusManager;
import java.util.HashSet;
import java.util.Set;
import javax.swing.JButton;
import javax.swing.KeyStroke;
public class Main {
  public static void main(String[] argv) throws Exception {
    JButton component = new JButton("a");
    Set set = new HashSet(component
        .getFocusTraversalKeys(KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS));
    set.add(KeyStroke.getKeyStroke("F2"));
    component.setFocusTraversalKeys(KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS, set);
  }
}

Determining If a Focus Lost Is Temporary or Permanent

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

Determining the Opposite Component of a Focus Event

  
import java.awt.ruponent;
import java.awt.event.FocusAdapter;
import java.awt.event.FocusEvent;
import javax.swing.JButton;
import javax.swing.JFrame;
public class Main {
  public static void main(String[] argv) throws Exception {
    JButton component = new JButton("a");
    component.addFocusListener(new MyFocusListener());
    JFrame f = new JFrame();
    f.add(component);
    f.pack();
    f.setVisible(true);
  }
}
class MyFocusListener extends FocusAdapter {
  public void focusGained(FocusEvent evt) {
    Component c = evt.getOppositeComponent();
    System.out.println(c.getName());
  }
  public void focusLost(FocusEvent evt) {
    Component c = evt.getOppositeComponent();
    System.out.println(c.getName() + "Opposite Component");
  }
}

Finding the Next Focusable Component

  
import java.awt.ruponent;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.FocusTraversalPolicy;
import java.awt.KeyboardFocusManager;
import javax.swing.JButton;
import javax.swing.JFrame;
public class Main {
  public static void main(String[] argv) {
    JFrame frame = new JFrame();
    JButton component1 = new JButton("1");
    JButton component2 = new JButton("2");
    JButton component3 = new JButton("3");
    frame.setLayout(new FlowLayout());
    frame.add(component1);
    frame.add(component2);
    frame.add(component3);
    frame.pack();
    frame.setVisible(true);
    System.out.println(findNextFocus().getName());
  }
  public static Component findNextFocus() {
    Component c = KeyboardFocusManager.getCurrentKeyboardFocusManager().getFocusOwner();
    Container root = c.getFocusCycleRootAncestor();
    FocusTraversalPolicy policy = root.getFocusTraversalPolicy();
    Component nextFocus = policy.getComponentAfter(root, c);
    if (nextFocus == null) {
      nextFocus = policy.getDefaultComponent(root);
    }
    return nextFocus;
  }
}

Find the previous focusable component

  
import java.awt.ruponent;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.FocusTraversalPolicy;
import java.awt.KeyboardFocusManager;
import javax.swing.JButton;
import javax.swing.JFrame;
public class Main {
  public static void main(String[] argv) {
    JFrame frame = new JFrame();
    JButton component1 = new JButton("1");
    JButton component2 = new JButton("2");
    JButton component3 = new JButton("3");
    frame.setLayout(new FlowLayout());
    frame.add(component1);
    frame.add(component2);
    frame.add(component3);
    frame.pack();
    frame.setVisible(true);
    System.out.println(findPrevFocus().getName());
  }
  public static Component findPrevFocus() {
    Component c = KeyboardFocusManager.getCurrentKeyboardFocusManager().getFocusOwner();
    Container root = c.getFocusCycleRootAncestor();
    FocusTraversalPolicy policy = root.getFocusTraversalPolicy();
    Component prevFocus = policy.getComponentBefore(root, c);
    if (prevFocus == null) {
      prevFocus = policy.getDefaultComponent(root);
    }
    return prevFocus;
  }
}

JComponent.setFocusTraversalKeys(int arg0, Set<? extends AWTKeyStroke> arg1)

  
import java.awt.AWTKeyStroke;
import java.awt.KeyboardFocusManager;
import java.util.HashSet;
import java.util.Set;
import javax.swing.JButton;
import javax.swing.KeyStroke;
public class Main {
  public static void main(String[] argv) throws Exception {
    JButton component = new JButton("a");
    Set<AWTKeyStroke> set = new HashSet<AWTKeyStroke>(component
        .getFocusTraversalKeys(KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS));
    set.add(KeyStroke.getKeyStroke("F2"));
    component.setFocusTraversalKeys(KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS, set);
  }
}

KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS

  
import java.awt.AWTKeyStroke;
import java.awt.KeyboardFocusManager;
import java.util.HashSet;
import java.util.Set;
import javax.swing.KeyStroke;
public class Main {
  public static void main(String[] argv) throws Exception {
    Set<AWTKeyStroke> set = new HashSet<AWTKeyStroke>(KeyboardFocusManager
        .getCurrentKeyboardFocusManager().getDefaultFocusTraversalKeys(
            KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS));
    set.add(KeyStroke.getKeyStroke("F3"));
    KeyboardFocusManager.getCurrentKeyboardFocusManager().setDefaultFocusTraversalKeys(
        KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS, set);
  }
}

KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS

  
import java.awt.KeyboardFocusManager;
import java.util.HashSet;
import java.util.Set;
import javax.swing.JButton;
import javax.swing.KeyStroke;
public class Main {
  public static void main(String[] argv) throws Exception {
    JButton component = new JButton("a");
    Set set = new HashSet(component
        .getFocusTraversalKeys(KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS));
    set.add(KeyStroke.getKeyStroke("F2"));
    component.setFocusTraversalKeys(KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS, set);
  }
}

KeyboardFocusManager.getCurrentKeyboardFocusManager().getDefaultFocusTraversalKeys(KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS)

  
import java.awt.AWTKeyStroke;
import java.awt.KeyboardFocusManager;
import java.util.HashSet;
import java.util.Set;
import javax.swing.KeyStroke;
public class Main {
  public static void main(String[] argv) throws Exception {
    Set<AWTKeyStroke> set = new HashSet<AWTKeyStroke>(KeyboardFocusManager
        .getCurrentKeyboardFocusManager().getDefaultFocusTraversalKeys(
            KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS));
    set.add(KeyStroke.getKeyStroke("F3"));
    KeyboardFocusManager.getCurrentKeyboardFocusManager().setDefaultFocusTraversalKeys(
        KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS, set);
  }
}

Listening to All Focus Changes Between Components and windows

 
import java.awt.ruponent;
import java.awt.KeyboardFocusManager;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
public class Main {
  public static void main(String[] argv) {
    KeyboardFocusManager.getCurrentKeyboardFocusManager().addPropertyChangeListener(
        new FocusChangeListener());
  }
}
class FocusChangeListener implements PropertyChangeListener {
  public void propertyChange(PropertyChangeEvent evt) {
    Component oldComp = (Component) evt.getOldValue();
    Component newComp = (Component) evt.getNewValue();
    if ("focusOwner".equals(evt.getPropertyName())) {
      if (oldComp == null) {
        System.out.println(newComp.getName());
      } else {
        System.out.println(oldComp.getName());
      }
    } else if ("focusedWindow".equals(evt.getPropertyName())) {
      if (oldComp == null) {
        System.out.println(newComp.getName());
      } else {
        System.out.println(oldComp.getName());
      }
    }
  }
}

Modify a component: press space bar or F2 to move focus to next focusable component.

  
import java.awt.ruponent;
import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.KeyStroke;
public class Main {
  public static void main(String[] argv) {
    JButton component = new JButton();
    NextFocusAction nextFocusAction = new NextFocusAction();
    component.getInputMap(JComponent.WHEN_FOCUSED).put(KeyStroke.getKeyStroke("SPACE"),
        nextFocusAction.getValue(Action.NAME));
    component.getInputMap(JComponent.WHEN_FOCUSED).put(KeyStroke.getKeyStroke("F2"),
        nextFocusAction.getValue(Action.NAME));
    component.getActionMap().put(nextFocusAction.getValue(Action.NAME), nextFocusAction);
    
  }
}
class NextFocusAction extends AbstractAction {
  public NextFocusAction() {
    super("Move Focus Forwards");
  }
  public void actionPerformed(ActionEvent evt) {
    ((Component) evt.getSource()).transferFocus();
  }
}

Null is returned if none of the components in this application has the focus

  
import java.awt.ruponent;
import java.awt.KeyboardFocusManager;
public class Main {
  public static void main() {
    Component compFocusOwner = KeyboardFocusManager.getCurrentKeyboardFocusManager()
        .getFocusOwner();
  }
}

Null is returned if none of the windows in this application has the focus

  
import java.awt.KeyboardFocusManager;
import java.awt.Window;
public class Main {
  public static void main() {

    Window windowFocusOwner =
    KeyboardFocusManager.getCurrentKeyboardFocusManager().getFocusedWindow();
  }
}

Press shift space or shift F2 to move the focus to the previous focusable component.

  
import java.awt.ruponent;
import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.KeyStroke;
public class Main {
  public static void main(String[] argv) {
    JButton component = new JButton();
    PrevFocusAction prevFocusAction = new PrevFocusAction();
    component.getInputMap(JComponent.WHEN_FOCUSED).put(KeyStroke.getKeyStroke("shift F2"),
        prevFocusAction.getValue(Action.NAME));
    component.getInputMap(JComponent.WHEN_FOCUSED).put(KeyStroke.getKeyStroke("shift SPACE"),
        prevFocusAction.getValue(Action.NAME));
    component.getActionMap().put(prevFocusAction.getValue(Action.NAME), prevFocusAction);
  }
}
class PrevFocusAction extends AbstractAction {
  PrevFocusAction() {
    super("Move Focus Backwards");
  }
  public void actionPerformed(ActionEvent evt) {
    ((Component) evt.getSource()).transferFocusBackward();
  }
}

Preventing a Component from Gaining the Focus

 
import javax.swing.JFrame;
public class Main {
  public static void main(String[] argv) throws Exception {
    JFrame frame = new JFrame();
    frame.setFocusable(false);
  }
}

Remove all backward focus traversal keys for the application

  

import java.awt.AWTKeyStroke;
import java.awt.KeyboardFocusManager;
import java.util.HashSet;
import java.util.Set;
public class Main {
  public static void main(String[] argv) throws Exception {
    Set<AWTKeyStroke> set = new HashSet<AWTKeyStroke>();
 
    KeyboardFocusManager.getCurrentKeyboardFocusManager().setDefaultFocusTraversalKeys(
        KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS, set);
  }
}

Remove all forward focus traversal keys for the application

  
import java.awt.AWTKeyStroke;
import java.awt.KeyboardFocusManager;
import java.util.HashSet;
import java.util.Set;
public class Main {
  public static void main(String[] argv) throws Exception {
    Set<AWTKeyStroke> set = new HashSet<AWTKeyStroke>();
    KeyboardFocusManager.getCurrentKeyboardFocusManager().setDefaultFocusTraversalKeys(
        KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS, set);
 
  }
}

Removing the Focus from the Application

  
import java.awt.KeyboardFocusManager;
public class Main {
  public static void main(String[] argv) throws Exception {
    KeyboardFocusManager.getCurrentKeyboardFocusManager().clearGlobalFocusOwner();
  }
}

Setting Focus Traversal Keys for the Entire Application

  
import java.awt.AWTKeyStroke;
import java.awt.KeyboardFocusManager;
import java.util.HashSet;
import java.util.Set;
import javax.swing.KeyStroke;
public class Main {
  public static void main(String[] argv) throws Exception {
    Set<AWTKeyStroke> set = new HashSet<AWTKeyStroke>(KeyboardFocusManager
        .getCurrentKeyboardFocusManager().getDefaultFocusTraversalKeys(
            KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS));
    set.add(KeyStroke.getKeyStroke("F2"));
    KeyboardFocusManager.getCurrentKeyboardFocusManager().setDefaultFocusTraversalKeys(
        KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS, set);
  }
}

Setting Focus Traversal Keys in a Component

  
import java.awt.KeyboardFocusManager;
import java.util.HashSet;
import java.util.Set;
import javax.swing.JButton;
import javax.swing.KeyStroke;
public class Main {
  public static void main(String[] argv) throws Exception {
    JButton component = new JButton("a");
    Set set = new HashSet(component
        .getFocusTraversalKeys(KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS));
    set.add(KeyStroke.getKeyStroke("F2"));
    component.setFocusTraversalKeys(KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS, set);
  }
}

Setting the Initial Focused Component in a Window

  
import java.awt.ruponent;
import java.awt.FlowLayout;
import java.awt.Window;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JButton;
import javax.swing.JFrame;
public class Main {
  public static void main(String[] argv) throws Exception {
    JFrame frame = new JFrame();
    JButton component1 = new JButton("1");
    JButton component2 = new JButton("2");
    JButton component3 = new JButton("3");
    frame.setLayout(new FlowLayout());
    frame.add(component1);
    frame.add(component2);
    frame.add(component3);
    InitialFocusSetter.setInitialFocus(frame, component2);
    frame.pack();
    frame.setVisible(true);
  }
}
class InitialFocusSetter {
  public static void setInitialFocus(Window w, Component c) {
    w.addWindowListener(new FocusSetter(c));
  }
}
class FocusSetter extends WindowAdapter {
  Component initComp;
  FocusSetter(Component c) {
    initComp = c;
  }
  public void windowOpened(WindowEvent e) {
    initComp.requestFocus();
    e.getWindow().removeWindowListener(this);
  }
}

Use Focus Events in Swing

  
 
import java.awt.Dimension;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import java.util.Vector;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextField;
public class Main extends JPanel implements FocusListener {
  public Main() {
    JTextField textField = new JTextField("A TextField");
    textField.addFocusListener(this);
    JLabel label = new JLabel("A Label");
    label.addFocusListener(this);
    add(label);
    String comboPrefix = "ComboBox Item #";
    final int numItems = 15;
    Vector vector = new Vector(numItems);
    for (int i = 0; i < numItems; i++) {
      vector.addElement(comboPrefix + i);
    }
    JComboBox comboBox = new JComboBox(vector);
    comboBox.addFocusListener(this);
    add(comboBox);
    JButton button = new JButton("A Button");
    button.addFocusListener(this);
    add(button);
    String listPrefix = "List Item #";
    Vector listVector = new Vector(numItems);
    for (int i = 0; i < numItems; i++) {
      listVector.addElement(listPrefix + i);
    }
    JList list = new JList(listVector);
    list.setSelectedIndex(1); 
    list.addFocusListener(this);
    JScrollPane listScrollPane = new JScrollPane(list);
    listScrollPane.getVerticalScrollBar().setFocusable(false);
    listScrollPane.getHorizontalScrollBar().setFocusable(false);
    add(listScrollPane);
    setPreferredSize(new Dimension(450, 450));
    setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
  }
  void displayMessage(String prefix, FocusEvent e) {
    System.out.println(prefix
        + (e.isTemporary() ? " (temporary):" : ":")
        + e.getComponent().getClass().getName()
        + "; Opposite component: "
        + (e.getOppositeComponent() != null ? e.getOppositeComponent().getClass().getName()
            : "null") );
  }
  public static void main(String[] args) {
    JFrame frame = new JFrame("FocusEventDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JComponent newContentPane = new Main();
    newContentPane.setOpaque(true); // content panes must be opaque
    frame.setContentPane(newContentPane);
    frame.pack();
    frame.setVisible(true);
  }
  public void focusGained(FocusEvent e) {
    displayMessage("Focus gained", e);
}
public void focusLost(FocusEvent e) {
    displayMessage("Focus lost", e);
}
}

Validating a JTextField When Permanently Losing the Focus

  
import java.awt.FlowLayout;
import java.awt.event.FocusAdapter;
import java.awt.event.FocusEvent;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.text.JTextComponent;
public class Main {
  public static void main(String[] argv) throws Exception {
    JTextField component = new JTextField(10);
    JTextField component1 = new JTextField(10);
    component.addFocusListener(new MyFocusListener());
    component1.addFocusListener(new MyFocusListener());
    JFrame f = new JFrame();
    f.setLayout(new FlowLayout());
    f.add(component1);
    f.add(component);
    f.pack();
    f.setVisible(true);
  }
}
class MyFocusListener extends FocusAdapter {
  boolean showingDialog = false;
  public void focusGained(FocusEvent evt) {
    final JTextComponent c = (JTextComponent) evt.getSource();
    String s = c.getText();
    for (int i = 0; i < s.length(); i++) {
      if (!Character.isDigit(s.charAt(i))) {
        c.setSelectionStart(i);
        c.setSelectionEnd(i);
        break;
      }
    }
  }
  public void focusLost(FocusEvent evt) {
    final JTextComponent c = (JTextComponent) evt.getSource();
    String s = c.getText();
    if (evt.isTemporary()) {
      return;
    }
    for (int i = 0; i < s.length(); i++) {
      if (!Character.isDigit(s.charAt(i))) {
        System.out.println("must only contain digits");
        c.requestFocus();
        break;
      }
    }
  }
}