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NFC Bricklet listener


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Hi Rik,

Regardless of the programming language, my advice would be to use a callback.

But the current documentation does not mention callbacks for this Bricklet and Java.

The docs mention callbacks for Java and other devices (example: Accelerometer Bricklet 2.0), and for the NFC Bricklet and another language like Ruby.

Maybe something is wrong with the documentation?

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ExampleScanForTags already uses callbacks, that's not the point here.

The point is that ExampleScanForTags just outputs every tag that was found, even if that tag doesn't change, it just repeats the output over and over again.

Here is a modified ExampleScanForTags that doesn't repeat the output if the tag didn't change:

import com.tinkerforge.IPConnection;
import com.tinkerforge.BrickletNFC;

public class ExampleScanForTags {
	private static final String HOST = "localhost";
	private static final int PORT = 4223;

	// Change XYZ to the UID of your NFC Bricklet
	private static final String UID = "X5a";

	// Note: To make the example code cleaner we do not handle exceptions. Exceptions
	//       you might normally want to catch are described in the documentation
	public static void main(String args[]) throws Exception {
		IPConnection ipcon = new IPConnection(); // Create IP connection
		// Note: Declare nfc as final, so the listener can access it
		final BrickletNFC nfc = new BrickletNFC(UID, ipcon); // Create device object

		ipcon.connect(HOST, PORT); // Connect to brickd
		// Don't use device before ipcon is connected

		// Add reader state changed listener
		nfc.addReaderStateChangedListener(new BrickletNFC.ReaderStateChangedListener() {
			private String lastTag = "";

			public void readerStateChanged(int state, boolean idle) {
				if(state == BrickletNFC.READER_STATE_REQUEST_TAG_ID_READY) {
					try {
						int i = 0;
						StringBuilder tagBuilder = new StringBuilder();
						BrickletNFC.ReaderGetTagID ret = nfc.readerGetTagID();

						for (int v: ret.tagID) {
							tagBuilder.append(String.format("0x%02X", v));

							if (i < ret.tagID.length - 1) {
								tagBuilder.append(" ");


						String tag = tagBuilder.toString();

						if (!lastTag.equals(tag)) {
							System.out.format("Found tag of type %d with ID [%s]\n", ret.tagType, tag);

							lastTag = tag;
					catch (Exception e) {

				if (idle) {
					try {
					catch (Exception e) {

		// Enable reader mode

		System.out.println("Press key to exit"); System.in.read();


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