Java is the technology of choice for building applications using managed code that can execute on mobile devices.
Android is an open source software platform and Linux-based operating system for mobile devices. The Android platform allows developers to write managed code using Java to manage and control the Android device.
Firebase is a Backend-as-a-Service that started as a startup and grew up into a next-generation app-development platform on Google Cloud Platform.
Firebase frees developers to focus crafting fantastic user experiences. You don’t need to manage servers. You don’t need to write APIs. Firebase is your server, your API and your datastore, all written so generically that you can modify it to suit most needs.