Petit exemple ici :

import java.awt.FlowLayout;

import javax.swing.JFrame;
import javax.swing.JFormattedTextField;
import javax.swing.JPanel;
import javax.swing.text.MaskFormatter;

public class TestFormatage extends JFrame{
	public TestFormatage(){
		super();
		JFormattedTextField jtf = new JFormattedTextField(createFormatter("######"));
		jtf.setColumns(10);
		JPanel contentPane = (JPanel)getContentPane();
		contentPane.setLayout(new FlowLayout());
		contentPane.add(jtf);
		setSize(300, 400);
		setVisible(true);
	}
	
	private MaskFormatter createFormatter(String s) {
	    MaskFormatter formatter = null;
	    try {
	        formatter = new MaskFormatter(s);
	    } catch (java.text.ParseException exc) {
	        System.err.println("formatter is bad: " + exc.getMessage());
	        System.exit(-1);
	    }
	    return formatter;
	}
	
	public static void main(String args[]){
		new TestFormatage();
	}
}