This is a basic Android Application that is connected throught the MQTT Protocol.
In order to configure and test the application, you need to go to file "MQTTConfiguration.java" in app/src/main/java/com/example/mqtt/service folder and set the URL of your MQTT Broker.
To use the application it is needed to have deployed a MQTT Broker (it does not matter what kind of broker: HiveMQ, Mosquitto, etc.) and set the Broker IP in the file mentioned previously.
Once the broker is deployed, run the application and test connecting to the broker clicking on "Connect", if the connection is succesful then you can publish messages in a specific topic.