Introduction to Java Programming 🚀

Welcome to the world of Java! In this lesson, you’ll set up your development environment, learn the basic structure of a Java program, and write your very first "Hello, World!" application. We’ll also explore how Java code runs behind the scenes and share a few fun facts about the language. This course will be using Java 24.

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1. Setting Up Your Development Environment

To write and run Java code, you need two main components:

1. Java Development Kit (JDK) – contains the compiler, Java Virtual Machine (JVM), and essential tools.
2. Integrated Development Environment (IDE) – software that makes coding easier with features like autocomplete, debugging, and project management.

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A. Installing the JDK

1. Download a Java 24-compatible JDK from: OpenJdk for OpenJDK.

2. Choose the correct installer for your operating system (Windows, macOS, Linux). 3.Follow the setup instructions.

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B. Installing IntelliJ IDEA

We’ll use IntelliJ IDEA Community Edition (free) for this course.

1. Download from the JetBrains website.
2. Install it using the provided installer.
3. On first launch, configure IntelliJ to use the JDK you installed.

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2. Anatomy of a Java Program

A simple Java program has a specific structure. Here’s an example:

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

Breaking it down:

• public class HelloWorld Declares a class named HelloWorld.

  • In Java, all code lives inside a class.
  • The file name must match the class name (e.g., HelloWorld.java).
  • public means the class is accessible from anywhere.

• public static void main(String[] args) The entry point of a Java program.

  • public → accessible from anywhere.
  • static → belongs to the class, not an instance which allows the method to be called without creating an object of the class (the JVM needs to call it directly).
  • void → doesn’t return a value.
  • main → special method name that JVM looks for.
  • (String[] args) → accepts command-line arguments as an array of strings.

• System.out.println("Hello, World!"); Prints text to the console.

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3. Writing Your First Program

1. Open IntelliJ IDEA and create a new project.
2. Create a new Java class named HelloWorld.
3. Type in the following code:

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

4. Click the green Run button next to main. You should see:

Hello, World!

🎉 Congratulations — you’ve just written your first Java program!

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4. How Java Code Runs

Java is both compiled and interpreted:

1. Compilation

   • The Java compiler (javac) translates .java source files into bytecode (.class files).
   • Bytecode is platform-independent.

2. Execution

   • The JVM reads the bytecode and translates it into machine code for your operating system (using an interpreter or Just-In-Time compiler).
   • This is why Java follows the "Write Once, Run Anywhere" principle.

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5. Fun Facts About Java

• Creator: James Gosling at Sun Microsystems, mid-1990s.
• Original Name: Oak (after a tree outside Gosling’s office).
• Why "Java"? Named after Java coffee from Indonesia.
• Platform-Independent: Runs on Windows, macOS, Linux, and more — no code changes needed.
• Everywhere: Powers Android apps, enterprise systems, big data tools, and even embedded devices.

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6. Course Structure

This course will take you from beginner to intermediate Java developer in three parts:

Part 1: Fundamentals

• The Java Type System
• Building a Small Project
• Control Flow (Conditionals & Loops)
• Clean Coding Techniques
• Debugging
• Packaging Your Code

Part 2: Object-Oriented Programming (OOP)

• Classes & Objects
• Inheritance
• Polymorphism
• Abstraction
• Encapsulation

Part 3: Advanced Concepts

• Functional Programming in Java
• Multithreading
• ExecutorService

Part 4: Async java

• CompletableFuture

✅ By the end of this course, you’ll be confident in writing Java programs, understanding how they work, and applying best practices.