Working with asynchronous notifications and callbacks in Java

The following lines continue the declaration of the public static main method. The code file for the sample is included in the mqtt_essentials_gaston_hillar_04 folder, in the Java01/src/Main.java file:

mqttAsyncClient.setCallback(new MqttCallback() {
				@Override
				public void connectionLost(Throwable cause) {
					cause.printStackTrace();
				}

				@Override
				public void deliveryComplete(IMqttDeliveryToken token) {
				}

				@Override
				public void messageArrived(String topic, MqttMessage message) throws Exception {
					if (!topic.equals(topic_for_led01)) {
						return;
					}
					String messageText = 
						new String(message.getPayload(), "UTF-8");
					System.out.println(
						String.format("Topic: %s. Payload: %s",
							topic,
							messageText));
				}
			});

The code calls the mqttAsyncClient.setCallback method with an anonymous subclass of the MqttCallback class as an argument. The setCallback method requires...