Tricky behaviour on JFormattedTextField

Question

Dear friends,
after few trials using JFormattedTextField, I finaly figured out how it beaves...
if you have te value 1,00 and type DEL with the cursor just before the comma character, the text field value becomes 100,00 - this weird behaviour has a simple explanation: when you click DEL before the comma symbol, the text component remove the comma, and the value 1,00 becomes 100. After that, the view formatter add the comma again and the value becomes 100,00. Strange ? yes, very strange behaviour... at least from the point of view of the user. My user is asking me: "Why 1 dolar becomes a hundred dollars in a unique touch?"
my question now is: How can I avoid that behaviour ? <b>how can I avoid the value 1,00 to be transformed into 100,00 by clicking DEL before the comma?</b> is it possible ?
below is my test code:
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.math.BigDecimal;
import java.text.DecimalFormat;
import java.text.DecimalFormatSymbols;
import java.util.Locale;
import javax.swing.JButton;
import javax.swing.JFormattedTextField;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingConstants;
import javax.swing.text.DefaultFormatterFactory;
import javax.swing.text.NumberFormatter;
public class testeFormat {
     public static JLabel getText = new JLabel("getText  = ");
     public static JLabel getValue = new JLabel("getValue = ");
     public static void main(String args[]) {
          JFrame frame = new JFrame();
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          frame.getContentPane().setLayout(new GridLayout(4, 1));
          final JFormattedTextField tf = new JFormattedTextField();
          DecimalFormat df = new DecimalFormat("#,###.00");
          df.setDecimalFormatSymbols(new DecimalFormatSymbols(new Locale("pt", "BR")));
          NumberFormatter nf = new NumberFormatter(df);
          nf.setValueClass(BigDecimal.class);
          nf.setOverwriteMode(false);
          DefaultFormatterFactory factory = new DefaultFormatterFactory(
                    //new NumberFormatter(df), // Default
                    nf, // Display
                    nf); // Edit
          tf.setFormatterFactory(factory);
          tf.setHorizontalAlignment(SwingConstants.RIGHT);
          nf.setAllowsInvalid(false);
          tf.setValue(new Double(0.0d));
          tf.setColumns(20);
          frame.getContentPane().add(tf);
          JButton button = new JButton("Test");
          frame.getContentPane().add(button);
          frame.getContentPane().add(getText);
          frame.getContentPane().add(getValue);
          button.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e) {
                    getText.setText("getText() = " + tf.getText());
                    getValue.setText("getValue() = " + tf.getValue());
          frame.setSize(new Dimension(300, 200));
          frame.setVisible(true);
}

Answer 1

you could add a keyListener
    tf.addKeyListener(new KeyAdapter(){
      public void keyPressed(KeyEvent ke){
        if(ke.getKeyCode() == KeyEvent.VK_DELETE)
          if(tf.getText().charAt(tf.getCaretPosition()) == ',')
            ke.consume();
            java.awt.Toolkit.getDefaultToolkit().beep();
        }}});