Validating longbox

/**
 * Constraint for comparing the value from a <b>textbox</b>.<br>
 * Throws an error message if NOT empty or NOT only numbers ( 0-9 ). Used in the
 * PayConditions Searchbox for checking that the SearchToken is only integers or
 * empty</br> </br>
 * 
 * <pre>
 * Java call:</br>
 * 		Textbox searchField = new Textbox();
 * 		searchField.setConstraint(new OnlyEmptyAndIntegerConstraint());
 * </pre>
 * 
 * @author Stephan Gerth
 */
public class OnlyEmptyAndIntegerConstraint implements Constraint, java.io.Serializable {

	private static final long serialVersionUID = 4052163775381888061L;

	public OnlyEmptyAndIntegerConstraint() {
		super();
	}

	@Override
	public void validate(Component comp, Object value) throws WrongValueException {

		if (comp instanceof Textbox) {

			// no need for checking ?
			if (((Textbox) comp).isDisabled()) {
				return;
			}

			// cast the value to String and trim it.
			final String enteredValue = ((String) value).trim();

			// check if not empty
			if (!enteredValue.isEmpty()) {
				// check if not allowed signs
				if (!enteredValue.matches("(([0-9]+)?)+")) {
					throw new WrongValueException(comp, Labels.getLabel("message.error.OnlyNumbersOrEmptyAllowed"));
				}
			}

		}
	}
}

// Check for numbers
// --------------------
// if ("-2324.00".matches("((-|\\+)?[0-9]+(\\.[0-9]+)?)+")) {
// System.out.println("Is a number");
// } else {
// System.out.println("Is not a number");
// }