Overview

The Java Development Kit (JDK) and Java Runtime Environment (JRE) include the basic components used to develop Java applications & libraries and to run Java applications. These components are organized as follows:

• Java Development Kit (JDK)
  • Development tools
  • Java Runtime Environment (JRE)
    • Runtime tools
    • Java Class Library (JCL)
    • Java Virtual Machine (JVM)

Note that there’s a hierarchical relationship between these components: The JCL and JVM are included in the JRE, which is itself included in the JDK.

Contents

This resource presents an overview of key elements and features—a small but important subset—of the JRE & JDK.¹ This overview may be accompanied by simple exercises, executed in a shell (Bash in OS X or Linux, Git Bash or Command Prompt in Windows), and using a simple text editor. The reason for this choice of environments is simple: When we use an IDE (such as IntelliJ IDEA, NetBeans, or Eclipse), many details of the interaction of the IDE with the JRE & JDK are hidden from us. For this introduction, it’s important that we understand some of these details that are usually hidden from us.

The tasks that may accompany this material will vary, depending on available time and interest, but they will typically include:

• Using JShell to execute simple Java code fragments interactively.
• Getting information on available options for the Java compiler from the compiler itself.
• Writing a simple Java program in a text editor, then compiling it and running it from the command line.
• Adding Javadoc comments to the source code, and generating technical documentation (in HTML format) from the comments.
• Modifying the program by moving it from the default package to a specified package, and recompiling it, to see the relationship between packages and directories.
• Getting information on available options for the Java application launcher from the launcher itself.
• Running our program—no longer in the default package—from the command line.
• Modifying our program to read and process values read from the command line.
• Modifying our program by invoking a static method of a class in the JCL, and by creating an instance of another class and invoking a method on that instance.
• Modifying our program to read and process values read from system properties.
• Creating a Java Archive (JAR) containing our compiled class file.
• Launching our application from the JAR file, passing arguments and system properties.

Requirements

There are no special setup requirements for reading the content of this module. However, to complete any accompanying tasks, JDK 11 or higher must be installed and configured, so that the JAVA_HOME environment variable refers to the JDK installation directory, and so that the bin subdirectory of the directory referenced by JAVA_HOME is included in the PATH environment variable.

1. There’s a significant overlap between the subset addressed here and the Java platform questions typically included in the Oracle Java Programmer I certification exam. ↩