IMEI Validator

import javafx.scene.Scene;
import javafx.stage.Stage;
import javafx.geometry.Pos;
import javafx.scene.layout.VBox;
import java.util.stream.IntStream;
import javafx.scene.control.Label;
import javafx.scene.control.Button;
import javafx.application.Application;
import javafx.scene.control.TextField;

/**
 *
 *
 * @author Aamir khan
 */
public class IMEIValidaotrApp extends Application {

    //components
    IMEIField field;
    Label status;
    VBox root;
    Button checkBtn;

    //this is a bad idea use a separate css file indeed
    private final String INVALID_LABEL_CSS = "-fx-text-fill:white; "
            + "-fx-background-color: #E26868;"
            + "-fx-padding:5px;"
            + "-fx-border-width:1; -fx-border-color:#B63E5A;"
            + "-fx-font-size: 9pt;";

    private final String VALID_LABEL_CSS = "-fx-text-fill:white; "
            + "-fx-background-color: #20A286;"
            + "-fx-padding:5px;"
            + "-fx-border-width:1; -fx-border-color:#19B99A;"
            + "-fx-font-size: 9pt;";

    private final String CHECK_BUTTON_CSS = "-fx-background-color:#c3c4c4,"
            + "linear-gradient(#d6d6d6 50%, white 100%),"
            + "radial-gradient(center 50% -40%, radius 200%, #e6e6e6 45%, rgba(230,230,230,0) 50%);"
            + "-fx-background-radius: 30; -fx-background-insets: 0,1,1;"
            + "-fx-text-fill: black;"
            + "-fx-effect: dropshadow( three-pass-box , rgba(0,0,0,0.6) , 3, 0.0 , 0 , 1 );";

    @Override
    public void init() {

        field = new IMEIField();
        field.setText("490154203237518");//for the Demo

        status = new Label();

        checkBtn = new Button("Check");
        checkBtn.setDefaultButton(true);
        //disable the button if the length is less than 15
        checkBtn.disableProperty().bind(field.textProperty().length().lessThan(15));
        checkBtn.setStyle(CHECK_BUTTON_CSS);
    }

    @Override
    public void start(Stage window) throws Exception {

        root = new VBox(status, field, checkBtn);
        root.setAlignment(Pos.CENTER);
        root.setSpacing(5.0);
        root.setStyle("-fx-padding: 10; -fx-font-size: 18;");

        window.setScene(new Scene(root, 300, 200));
        window.setTitle("IMEI Checker");
        window.setResizable(false);
        window.show();

        checkBtn.setOnAction(e -> validateIMEI());

    }

    /**
     * implementation of
     * <a href = "https://en.wikipedia.org/wiki/Luhn_algorithm Luhn algorithm">Luhn
     * algorithm</a>
     * is also known as “Modulus 10” algorithm.<br>
     * It is a simple checksum formula used to validate a variety of
     * identification numbers,<br>
     * such as credit card numbers, IMEI numbers, National Provider Identifier
     * numbers in US and Canadian Social Insurance Numbers.<br>
     * It was created by IBM scientist Hans Peter Luhn.<br>
     * Verification is done by validating check digit.<br><br>
     *
     * <p>
     * simply Double the value of every second digit from the right end (first
     * right will be check digit number). Add the individual digits comprising
     * both the products from step (1) and unaffected digits in the original
     * number. If the total modulo 10 is equal to 0, then the number is valid,
     * else it is not valid. an example of IMEI no. 490154203237518</p>
     */
    private void validateIMEI() {

        final int[] numbers = field.getText().chars().map(this::ConvertASCIIToNumer).toArray();
        boolean isValid = IntStream.range(0, numbers.length)
                .map(i -> (((i % 2) ^ (numbers.length % 2)) == 0)
                        ? ((2 * numbers[i]) / 10 + (2 * numbers[i]) % 10)
                        : numbers[i])
                .sum() % 10 == 0;

        if (isValid) {
            status.setStyle(VALID_LABEL_CSS);
            status.setText("VALID");
        } else {
            status.setText("INVALID");
            status.setStyle(INVALID_LABEL_CSS);
        }
    }

    /**
     * Returns the numeric value of the ASCII
     */
    private int ConvertASCIIToNumer(int value) {
        return Character.digit(value, 10);
    }

    /**
     * a specific class for Holding
     * <a href =
     * "https://en.wikipedia.org/wiki/International_Mobile_Station_Equipment_Identity">
     * IMEI Numbers
     * </a>
     */
    class IMEIField extends TextField {

        private final int LIMIT = 15;//A Valid IMEI Number has 15 digits

        @Override
        public void replaceText(int start, int end, String text) {
            if (validate(text)) {
                super.replaceText(start, end, text);
                onLengthListener();
            }
        }

        @Override
        public void replaceSelection(String text) {
            if (validate(text)) {
                super.replaceSelection(text);
                onLengthListener();
            }
        }

        private void onLengthListener() {
            //Stop if user type more than LIMIT
            textProperty().
                    addListener((observable, oldValue, newValue) -> {
                        if (newValue.length() > LIMIT) {
                            setText(oldValue);
                        }
                    });

        }

        /**
         * Validate input against the {@link String} and make sure input is
         * Number only
         *
         * @return true if the value is a Numeric Value <b>0-9</b>
         */
        private boolean validate(String text) {

            //furtuhre check can be done for "Empty input" or for "White Space"
            //return (" ".equals(text) || "".equals(text) ||text.matches("[0-9]"));
            return ("".equals(text) || text.matches("[0-9]"));
        }

    }

    //Mr. Main
    public static void main(String[] args) {
        launch(args);//Entry point for the FX Thread

    }

}