Problem with Java and Button (GroveDigitalIn)

Hi the community,

I’m trying to use Java language with GrovePI. My development is based on the Software/Java8 directory.

All sensors from the GrovePi+ Starter kit are working in Java excepted the button sensor. I obtain always the same value even if I press the button.

I know the button sensor is working because I tested it with a Python program.

Here is a snippet which uses GrovePi API (Software/Java8).

public class Button {
    public static void main(String[] args) throws InterruptedException, IOException {
	GrovePi grovePi = new GrovePi4J();
	GroveDigitalIn led = grovePi.getDigitalIn(6);

	while (true) {
	    try {
	    } catch (IOException ex) {

Here is a snippet where I’ve isolated the problem (pure PI4J).

public class ButtonIssue {

    private static final int dRead_cmd = 1;
    private static final int unused = 0;
    private static final int GROVEPI_ADDRESS = 4;
    private static final byte PIN_MODE_COMMAND = 5;
    private static final byte PIN_MODE_INPUT = 0;
    private static final int PIN = 6;

    private I2CDevice device;
    public ButtonIssue() throws IOException, InterruptedException, UnsupportedBusNumberException {
	    I2CBus bus = I2CFactory.getInstance(I2CBus.BUS_1);
	    device = bus.getDevice(GROVEPI_ADDRESS);

	    writeI2c(PIN_MODE_COMMAND, PIN, PIN_MODE_INPUT, unused);

	    while (true) {
	        writeI2c(dRead_cmd, PIN, unused, unused);
	        System.out.println( & 0xff);

    public void writeI2c(int... bytes) throws IOException {
	    // Convert array: int[] to byte[]
	    final ByteBuffer byteBuffer = ByteBuffer.allocate(bytes.length);
	    for (int i = 0; i < bytes.length; i++) {
	        byteBuffer.put((byte) bytes[i]);
	    device.write(1, byteBuffer.array(), 0, byteBuffer.limit());

    public static void main(String[] args) throws IOException, InterruptedException, UnsupportedBusNumberException {
	    new ButtonIssue();

I supposed that writeI2c with read command has a problem. Maybe, someone can test these snippets to confirm this issue?