What is JDK (Java Development Kit)?

The Java Development Kit (JDK) is a software development package provided by Oracle (and other vendors) that contains everything you need to develop, compile, debug, and run Java applications. It includes tools such as the Java compiler (javac), Java Runtime Environment (JRE), libraries, and other essential utilities.

When we talk about Java development, the JDK is at the heart of it all. Whether you’re building desktop applications, web services, or Android apps, you’ll need the Java Development Kit to write and execute your code.

Let’s break down what the JDK is, why it matters, and what it includes.

1. What Exactly Is the JDK?

The Java Development Kit (JDK) is a comprehensive set of tools and components used by developers to build Java applications. It is a superset of the Java Runtime Environment (JRE). This means the JDK includes everything in the JRE (to run Java programs), plus development tools to write, compile, and debug code.

Without the JDK, you can run Java programs (via the JRE), but you can’t develop them.

2. What’s Included in the JDK?

The JDK comes packed with the following key components:

Java Compiler (`javac`)

Converts Java source code (.java files) into bytecode (.class files) that can be executed by the Java Virtual Machine (JVM).

Java Runtime Environment (JRE)

Includes the JVM and standard class libraries necessary to run Java applications.

Java Virtual Machine (JVM)

Responsible for running the bytecode, ensuring Java’s “write once, run anywhere” capability.

Development Tools

javac: Java compiler
java: Launcher for running Java programs
javadoc: Tool for generating documentation from code comments
jdb: Java debugger
jar: Tool for packaging files into JAR (Java Archive) files
jshell: Interactive Java shell (introduced in Java 9)

Core Java Libraries

Contains essential packages like java.lang, java.util, java.io, etc., required for building Java applications.

3. Different JDK Distributions

While Oracle provides the official JDK, there are several other OpenJDK-based distributions:

Oracle JDK – Commercial use may require a license for older versions.
OpenJDK – Open-source version of Java maintained by the community.
Amazon Corretto, Azul Zulu, AdoptOpenJDK (Eclipse Temurin) – Other free, production-ready JDK builds.

All these distributions are based on the same OpenJDK codebase and are functionally equivalent for most applications.

4. JDK Versions and LTS Releases

The JDK follows a 6-month release cycle, but some versions are designated as LTS (Long-Term Support). These are more stable and are maintained for several years:

JDK 8, JDK 11, JDK 17, and JDK 21 are the current LTS versions.
Developers should prefer LTS versions for production environments.

5. How to Use the JDK

Using the JDK typically involves:

Writing code in a .java file.
Compiling it with javac.
Running the bytecode with java.

Example:

javac HelloWorld.java
java HelloWorld

Developers can also use IDEs like IntelliJ IDEA, Eclipse, or NetBeans, which internally use the JDK to build and run projects.

6. Importance of JDK in Development

Essential for Developers: It’s the foundational toolset for building anything in Java.
Full Toolchain: Compiling, testing, packaging, and documenting Java applications.
Backbone of IDEs: All major Java IDEs require a JDK installation to work properly.
Enables Modern Features: Each JDK version includes new language enhancements, compiler optimizations, and better tools.

Key Points

The JDK is essential for Java development — includes compiler, runtime, libraries, and tools.
Without JDK, you cannot write or compile Java programs.
Contains the JRE and JVM, plus development utilities like javac, javadoc, and jdb.
Multiple JDK distributions are available: Oracle JDK, OpenJDK, Amazon Corretto, etc.
Use LTS versions (Java 8, 11, 17, 21) for production environments.
IDEs like IntelliJ and Eclipse require the JDK to function.
javac compiles Java code; java executes it.
JDK releases every 6 months, but LTS versions are more stable for long-term use.