Set place holder char for JFormattedTextField in Java

import java.awt.Container;
import java.text.ParseException;
// w w  w.  ja va2s . co m
import javax.swing.BoxLayout;
import javax.swing.JFormattedTextField;
import javax.swing.JFrame;
import javax.swing.text.MaskFormatter;

public class Main {
  public static void main(String args[]) throws ParseException {
    JFrame f = new JFrame();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    Container content = f.getContentPane();
    content.setLayout(new BoxLayout(content, BoxLayout.PAGE_AXIS));

    MaskFormatter mf1 = new MaskFormatter("###-###-###");
    mf1.setPlaceholderCharacter('_');
    JFormattedTextField ftf1 = new JFormattedTextField(mf1);
    content.add(ftf1);

    MaskFormatter mf2 = new MaskFormatter("(###) ###-####");
    JFormattedTextField ftf2 = new JFormattedTextField(mf2);
    content.add(ftf2);
    f.setSize(300, 100);
    f.setVisible(true);
  }
}