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import java.awt.BorderLayout;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class Main {
public static void main(String[] a) {
final JTextField textField = new JTextField(5);
textField.addFocusListener(new FocusListener() {
public void focusGained(FocusEvent e) {
}
public void focusLost(FocusEvent e) {
if (!e.isTemporary()) {
String content = textField.getText();
if (!content.equals("a") ) {
System.out.println("illegal value! " + content);
SwingUtilities.invokeLater(new FocusGrabber(textField));
}
}
}
});
JFrame frame = new JFrame();
frame.add(textField,BorderLayout.CENTER);
frame.setSize(300,300);
frame.setVisible(true);
}
}
class FocusGrabber implements Runnable {
private JComponent component;
public FocusGrabber(JComponent component) {
this.component = component;
}
public void run() {
component.grabFocus();
}
}
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