添加FocusListener监听
package events;
/*
* FocusEventDemo.java
*
*/
import java.util.Vector;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class FocusEventDemo extends JFrame
implements FocusListener {
final static String newline = "\n";
JTextArea display;
public FocusEventDemo(String name) {
super(name);
}
public void addComponentsToPane(final Container pane) {
GridBagLayout gridbag = new GridBagLayout();
pane.setLayout(gridbag);
GridBagConstraints c = new GridBagConstraints();
c.fill = GridBagConstraints.HORIZONTAL;
c.weightx = 1.0; //Make column as wide as possible.
JTextField textField = new JTextField("A TextField");
textField.setMargin(new Insets(0,2,0,2));
textField.addFocusListener(this);
gridbag.setConstraints(textField, c);
add(textField);
c.weightx = 0.1; //Widen every other column a bit, when possible.
c.fill = GridBagConstraints.NONE;
JLabel label = new JLabel("A Label");
label.setBorder(BorderFactory.createEmptyBorder(0,5,0,5));
label.addFocusListener(this);
gridbag.setConstraints(label, c);
add(label);
String comboPrefix = "ComboBox Item #";
final int numItems = 15;
Vector<String> vector = new Vector<String>(numItems);
for (int i = 0; i < numItems; i++) {
vector.addElement(comboPrefix + i);
}
JComboBox comboBox = new JComboBox(vector);
comboBox.addFocusListener(this);
gridbag.setConstraints(comboBox, c);
add(comboBox);
c.gridwidth = GridBagConstraints.REMAINDER;
JButton button = new JButton("A Button");
button.addFocusListener(this);
gridbag.setConstraints(button, c);
add(button);
c.weightx = 0.0;
c.weighty = 0.1;
c.fill = GridBagConstraints.BOTH;
String listPrefix = "List Item #";
Vector<String> listVector = new Vector<String>(numItems);
for (int i = 0; i < numItems; i++) {
listVector.addElement(listPrefix + i);
}
JList list = new JList(listVector);
list.setSelectedIndex(1); //It's easier to see the focus change
//if an item is selected.
list.addFocusListener(this);
JScrollPane listScrollPane = new JScrollPane(list);
gridbag.setConstraints(listScrollPane, c);
add(listScrollPane);
c.weighty = 1.0; //Make this row as tall as possible.
c.gridheight = GridBagConstraints.REMAINDER;
//Set up the area that reports focus-gained and focus-lost events.
display = new JTextArea();
display.setEditable(false);
//The setRequestFocusEnabled method prevents a
//component from being clickable, but it can still
//get the focus through the keyboard - this ensures
//user accessibility.
display.setRequestFocusEnabled(false);
display.addFocusListener(this);
JScrollPane displayScrollPane = new JScrollPane(display);
gridbag.setConstraints(displayScrollPane, c);
add(displayScrollPane);
setPreferredSize(new Dimension(450, 450));
((JPanel)pane).setBorder(BorderFactory.createEmptyBorder(20,20,20,20));
}
public void focusGained(FocusEvent e) {
displayMessage("Focus gained", e);
}
public void focusLost(FocusEvent e) {
displayMessage("Focus lost", e);
}
void displayMessage(String prefix, FocusEvent e) {
display.append(prefix
+ (e.isTemporary() ? " (temporary):" : ":")
+ e.getComponent().getClass().getName()
+ "; Opposite component: "
+ (e.getOppositeComponent() != null ?
e.getOppositeComponent().getClass().getName() : "null")
+ newline);
display.setCaretPosition(display.getDocument().getLength());
}
/**
* 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.
FocusEventDemo frame = new FocusEventDemo("FocusEventDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Set up the content pane.
frame.addComponentsToPane(frame.getContentPane());
//Display the window.
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
/* Use an appropriate Look and Feel */
try {
//UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
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();
}
});
}
}
