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

import java.awt.Toolkit;
import java.text.NumberFormat;
import java.text.ParseException;
import java.util.Locale;

public class WholeNumberField extends JTextField {

    private Toolkit toolkit;
    private NumberFormat integerFormatter;

    public WholeNumberField(int value, int columns) {
	super(columns);
	toolkit = Toolkit.getDefaultToolkit();
        integerFormatter = NumberFormat.getNumberInstance(Locale.US);
        integerFormatter.setParseIntegerOnly(true);
	setValue(value);
    }

    public int getValue() {
	int retVal = 0;
	try {
            retVal = integerFormatter.parse(getText()).intValue();
        } catch (ParseException e) {
            // This should never happen because insertString allows
            // only properly formatted data to get in the field.
            toolkit.beep();
	}
	return retVal;
    }

    public void setValue(int value) {
	setText(integerFormatter.format(value));
    }

    protected Document createDefaultModel() {
	return new WholeNumberDocument();
    }

    protected class WholeNumberDocument extends PlainDocument {

	public void insertString(int offs, String str, AttributeSet a) 
	    throws BadLocationException {

	    char[] source = str.toCharArray();
	    char[] result = new char[source.length];
	    int j = 0;

	    for (int i = 0; i < result.length; i++) {
		if (Character.isDigit(source[i]))
		    result[j++] = source[i];
		else {
		    toolkit.beep();
		    System.err.println("insertString: " + source[i]);
		}
	    }
	    super.insertString(offs, new String(result, 0, j), a);
	}
    }

}