It's important to note that this book focuses on JVM implementations compatible with Oracle's Java SE (Standard Edition) 8 (and higher) platform only. This version can be installed on desktop computers, servers, and many single-board computers (including all the models of the popular credit-card-sized Raspberry Pi). We will use Oracle's implementation in this book, but both the open source OpenJDK and IBM's own J9 Java SE implementations of the same version should work equally well.
The Java platform as published by Google on Android phones and tablets is not covered in this book at all. One of the reasons is that the Java version used on Android is based on an older version of Java. While progress has been made to make Android's version of the platform more up to date, it still doesn't have all the features of Oracle's Java SE 8, and it requires different compilers and tools. Another reason is that Google omitted a lot of the Java SE APIs and replaced them with their own unique, incompatible APIs. Some of the languages covered in this book can be used with Android, however. Kotlin, in particular, is a very popular choice for modern Android development. This use case will not be explored in this book, though.
