Developers who want to develop on a JVM should always install JDK. It bundles the Java Runtime Environment (JRE), the Java compiler, and various development tools, some of which we will explore in this chapter. Even if you are planning to do most of your JVM development in a language other than Java, it is strongly advised that you still install the complete JDK. Many prominent development tools require a fully installed JDK to run. Also, sooner or later, you'll probably want to use some of the tools that are only included in JDK.

The recent version of the Linux distribution of the Raspberry Pi installs the Java SE Embedded 8 JDK automatically when using the default Raspian installation options. Be aware though that, often, the supplied version is not up-to-date. We are not aware of other major operating systems that bundle JDK with their default installation. We will...

All JVM languages define their own syntaxes for creating classes and instantiating objects, but in the end, they produce class files that would run on the JVM. In order to be able to run on the JVM and be able to offer interoperability with classes written in other languages on the JVM platform, they have to follow JVM's requirements for organizing classes. We'll discuss the following topics:

• Packages
• Choosing a package
• Package examples
• Fully qualified class names

Most languages...

The Java Class Library is also simply known as the Java API. It's a huge collection of prebuilt classes that is distributed with the Java SE platform. Some of the more important themes of the library include:

• Definitions and implementations of common data structures
• Console I/O
• File I/O
• Mathematics
• Networking
• Regular expressions
• XML creation and processing
• Database access
• GUI toolkits
• Reflection

We cannot cover the complete Java Class Library here, but we want to give some examples of the APIs that are available and give you pointers on where to find the classes you need. Before we look at specific classes, we will take a look at the main organization. We'll cover the following topics:

• Java Class Library organization
• Package overview
• Fundamental classes from the java.lang package
• Collections API, namely java.util.ArrayList and java.util.HashMap
...

Running applications on a JVM is often considered a fairly complex topic. As mentioned in the previous chapter, compilers that target a JVM compile their source code to binary files with a .class file extension. There are a few rules that must be followed before you can have a JVM instance run the code inside the .class files:

• At least one class must have a static main() method
• All the class files should be stored in specific directories
• The ClassPath has to be specified
• Class files can optionally be placed inside a JAR archive container
• To run the program, the java command is used

We will take a quick look at each rule. Then, to demonstrate these concepts as clearly as possible, we will be doing a hands-on demonstration project in Java.

As we have seen in the previous section, using a simple text editor to create JVM programs can be a quite cumbersome process. In some languages, including Java, you'll have to make sure that the package name structure matches the directory structure of the source code. As we will soon see, there are more rules that some languages impose on the developer. Java requires that the source code filename should match the corresponding class name. Also, you have to manually specify the ClassPath when running programs. The list goes on.

In the JVM world, most programmers use the sophisticated IDE to develop their projects. Both commercial and open source IDEs that support the JVM concept are available on the market. Java support is extremely strong on all popular IDEs. Java programmers can expect the following features in a modern IDE:

• First is the autocompletion feature...