JSpinnerに関して

import java.text.*;
import javax.swing.*;
import javax.swing.text.*;

public class SPTest {

	public static void main(String[] args) throws Exception{
		JFrame f = new JFrame();
		f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		JPanel p = (JPanel)f.getContentPane();
		MaskFormatter mf = new MaskFormatter("****");
		mf.setValidCharacters("1234567890");
		NumberFormatter nf = new NumberFormatter(new DecimalFormat("0000")){
		    public String valueToString(Object value) throws ParseException {
		    	if(value != null && value instanceof String)
		    		return (String)value;
		    	else
		    		return super.valueToString(value);
		    }

		};
		JFormattedTextField ftf = new JFormattedTextField(new DefaultFormatterFactory(mf,nf));
		ftf.setFormatterFactory(new DefaultFormatterFactory(mf,nf));
		p.add(ftf);
		f.pack();
		f.show();
	}
}