What is JDK, Components and how it works

What is JDK?

JDK stands for Java Development Kit.

It is a software package that provides everything you need to write, compile, and run Java programs.

Think of the JDK as a toolbox for Java developers. Inside the box, you’ll find tools to write code, convert it to a format the machine understands, and run it.

Components of JDK

The JDK includes several important tools and libraries. Here's a simple breakdown:

JRE (Java Runtime Environment)

• It allows running Java programs.

• Contains:

  • JVM (Java Virtual Machine) – Runs Java bytecode.

  • Libraries – Pre-built Java code for tasks like reading files, networking, math, etc.

JVM (Java Virtual Machine)

• It executes the .class file (compiled Java bytecode).

• It makes Java platform-independent, meaning the same Java code runs on Windows, Linux, Mac, etc.

• Works with memory management, security, and performance.

Java Compiler (javac)

• Converts .java files (your code) into .class files (bytecode).

• example:

javac HelloWorld.java

Development Tools

• Tools like:

  • javadoc – Generates documentation.

  • javap – Shows the structure of class files.

  • jdb – Java debugger.

How Java Works (Step-by-Step)

Let’s understand what happens from writing code to running it:

Writing code

You write Java code in a file with a .java extension.

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Step 2: Compile the Code (javac)

Use the Java compiler to convert .java to .class (bytecode).

javac HelloWorld.java

✅ Output: A file HelloWorld.class is created.

Step 3: Run the Program (java)

Use the Java launcher to run the program.

java HelloWorld

✅ Output on the console:

Hello, World!

Behind the scenes:

• JVM loads the HelloWorld.class.

• It interprets or compiles the bytecode.

• Executes the code line by line.