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import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.InputVerifier;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JTextField;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.JTextComponent;
public class MainClass {
public static void main(String args[]) throws Exception {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JTextField nameTextField = new JTextField();
frame.add(nameTextField, BorderLayout.NORTH);
frame.add(new JTextField(), BorderLayout.SOUTH);
InputVerifier verifier = new InputVerifier() {
public boolean verify(JComponent input) {
final JTextComponent source = (JTextComponent) input;
String text = source.getText();
if ((text.length() != 0) && !(text.equals("Exit"))) {
JOptionPane.showMessageDialog(source, "Can't leave.", "Error Dialog",
JOptionPane.ERROR_MESSAGE);
return false;
} else {
return true;
}
}
};
nameTextField.setInputVerifier(verifier);
frame.setSize(250, 100);
frame.setVisible(true);
}
}
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