Java editions

Several editions of Java are available. Each one aims at different use cases. Some of the editions have had numerous name changes over the years; the current names of the editions are as follows:

• Java Standard Edition (Java SE)
• Java Enterprise Edition (Java EE)
• Java Micro Edition (Java ME)

Java SE

This is the most important edition. When people mention the term "Java," they usually refer to this edition. This book concentrates solely on the Java SE platform.

This edition is meant to run on desktop machines and servers, and as we will see later, an embedded version is also available and bundled with Raspberry Pi's Linux distribution. Java SE comes with the complete Java Class Library. It includes the classic Swing GUI Toolkit; most versions also contain the modern JavaFX GUI toolkit.

Note that a recent update of Java SE Embedded removed the JavaFX toolkit. Once you install this JDK update on the Raspberry Pi, the JavaFX component will be gone. Oracle has open sourced their JavaFX port for the Raspberry Pi so that advanced users can still download and compile it.

Java SE is mostly meant to create standalone consoles, desktop GUIs, or headless applications; alternatively, it is used to create external libraries.

Java EE

Java EE builds upon Java SE; therefore, it requires that Java SE is installed. It adds lots of APIs in a lot of categories. Java EE applications usually run inside JVM application servers. This book does not cover Java EE in depth but will mention it from time to time. This is because it is a very important addition to the Java platform, especially for business developers.

It is not possible to download a Java EE standalone edition from the Oracle website; instead, you will have to download a full application server that is compatible with the Java EE platform version you want to use. Some IDEs bundle the Java EE application server as well; we will cover this in the next chapter.

The Java EE standard only describes the APIs that must be available, but it does not dictate the implementation. It's up to the Java EE-compatible application servers to come up with actual implementations that adhere to these standards.

Example – Java Persistence API as implemented by two application servers

Java EE describes the Java Persistence API (JPA). It is an object relation mapper (ORM) API, a layer between Java objects and relational databases (often SQL databases, such as Oracle database, Oracle MySQL, PostgreSQL, and so on). With a few lines of code, the content of JVM objects can be written to the database or vice versa: read from the database and put in the object.

Oracle's own reference implementation of Java EE is an open source application server called GlassFish. GlassFish bundles the existing EclipseLink open source project as the implementer of the JPA standard. Meanwhile, Red Hat's WildFly, a different open source Java EE application server, bundles Red Hat's own, more popular, Hibernate ORM open source project, which also implements the JPA standard.

If developers only use the features documented in the JPA standard, then it should not matter to them which implementation is used, but problems arise once features are used that are unique to a specific implementation.

If you do not agree with the choices made by the vendor of your application server, it is often possible to switch implementations of a particular standard. Yes, JVM developers really love having choices!

Java ME

Before the days of iOS and Android, Java ME happened to be an important platform for feature phones and early smartphones for games and some basic applications. iOS and Android both never supported Java ME applications, so nowadays it does not play a major role anymore.

It featured a subset of the Java Class Library and offered some additional APIs to work with mobile devices. Java ME got a second life as Java ME Embedded, which can be used for commercial IoT devices.