JTextField: setInputVerifier(InputVerifier input)

 
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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JTextField: setInputVerifier(InputVerifier input) : JTextField « javax.swing « Java by API

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