👋 Java Hello World: Your First Program Guide

This guide covers how to write, compile, and run your first Java program — "Hello World" — using:

• ✅ Command Line (macOS/Linux/Windows)
• 🌀 Eclipse IDE
• 🧠 IntelliJ IDEA
• 💻 Visual Studio Code

💻 Understanding the Java Hello World Program

Let's break down the classic "Hello World" program in Java:

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

📝 Code Explanation

• public class HelloWorld: Defines a class named HelloWorld that can be accessed from anywhere
• public static void main(String[] args): The entry point method that Java looks for when running a program
  • public: Accessible from anywhere
  • static: Belongs to the class, not an instance
  • void: Returns no value
  • main: Special method name that Java recognizes as the starting point
  • String[] args: Command-line arguments passed to the program
• System.out.println("Hello, World!");: Prints the text "Hello, World!" to the console
  • System: A built-in class that provides access to the system
  • out: The standard output stream
  • println(): A method that prints text and adds a new line

🔧 Running Java Hello World from the Command Line

📝 Step 1: Save Your File

Save the code as HelloWorld.java. Important: The filename must match the class name exactly, including capitalization.

💡 Step 2: Compile the Program

Open Terminal (macOS/Linux) or Command Prompt (Windows) and navigate to the directory containing your file:

javac HelloWorld.java

This command invokes the Java compiler (javac), which converts your human-readable code into bytecode that the Java Virtual Machine (JVM) can understand. If successful, it creates a HelloWorld.class file.

▶️ Step 3: Run the Program

java HelloWorld

This command starts the JVM and executes your program. The output should be:

Hello, World!

⚠️ Common mistakes:

• Do not include .class or .java when running with the java command
• Make sure you're in the correct directory
• The class name and filename must match exactly (case-sensitive)

🔍 Troubleshooting Java Command Line Issues

🌀 Running Java in Eclipse IDE

🔧 Step 1: Create a Java Project

• Open Eclipse
• Go to File → New → Java Project
• Enter project name (e.g., HelloWorldProject)
• Click Finish

📦 Step 2: Add a Java Class

• Right-click on the src folder in the Project Explorer
• Select New → Class
• Enter HelloWorld as the class name
• Check the box "public static void main(String[] args)"
• Click Finish

✍️ Step 3: Enter Code

The editor will open with a template. Replace or modify the generated code so it looks like:

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

▶️ Step 4: Run

• Right-click the file in the Project Explorer → Run As → Java Application
• Alternatively, click the Run button (▶️) in the toolbar
• Output appears in the Console view at the bottom of the screen

🔍 Eclipse Tips

• Auto-format code: Press Ctrl+Shift+F (Windows/Linux) or Cmd+Shift+F (macOS)
• Quick fix errors: Hover over red underlines and press Ctrl+1 for suggestions
• Content assist: Press Ctrl+Space for code completion suggestions

🧠 Running Java in IntelliJ IDEA

🔧 Step 1: Create New Project

• Open IntelliJ IDEA
• Click New Project
• Choose Java from the left panel
• Select your JDK from the dropdown (or set up a new one)
• Click Next
• Set project name (e.g., HelloWorldApp)
• Click Finish

📂 Step 2: Add Java Class

• Right-click the src folder in the Project view → New → Java Class
• Name it HelloWorld

✍️ Step 3: Enter Code

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

▶️ Step 4: Run

• Click the green run triangle (▶️) in the gutter next to the main method
• Alternatively, right-click anywhere in the editor → Run 'HelloWorld.main()'
• Output shows in the Run tool window at the bottom

🔍 IntelliJ IDEA Tips

• Auto-format code: Press Ctrl+Alt+L (Windows/Linux) or Cmd+Option+L (macOS)
• Quick documentation: Press Ctrl+Q (Windows/Linux) or F1 (macOS) to view documentation
• Smart code completion: Press Ctrl+Shift+Space for context-aware suggestions

💻 Running Java in Visual Studio Code

🔧 Step 1: Install Extensions

• Open VS Code
• Go to Extensions view (click the square icon on the sidebar or press Ctrl+Shift+X)
• Search for "Extension Pack for Java" and install it

📂 Step 2: Create a Java Project

• Press Ctrl+Shift+P to open the Command Palette
• Type "Java: Create Java Project" and select it
• Choose "No build tools" for a simple project
• Select a location for your project
• Enter a project name (e.g., HelloWorldVSCode)

✍️ Step 3: Create a Java Class

• In the Explorer view, expand your project folder
• Right-click on the src folder → New File
• Name it HelloWorld.java
• Enter the Hello World code:

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

▶️ Step 4: Run

• Click the "Run" link that appears above the main method
• Alternatively, right-click in the editor → Run Java
• Output appears in the "Terminal" panel at the bottom

🔍 VS Code Java Tips

• Code actions: Hover over code and click the light bulb 💡 for quick fixes
• Debugging: Set breakpoints by clicking in the gutter and press F5 to debug
• Java Projects view: Click the Java Projects icon in the sidebar for a structured view

🎓 Summary

🔍 Common Errors and Solutions

🎯 Next Steps

After mastering the Hello World program, you're ready to:

1. Learn about Java variables and data types
2. Explore control flow statements like if-else and loops
3. Practice with more complex programs that use methods

Happy coding! 🎉