Additional Notes

🆔 Naming Conventions

• File name must match the public class name (e.g., Hello.java)

• Class names → PascalCase (e.g., MyFirstProgram)

• Method and variable names → camelCase (e.g., printMessage())

🌀 How Java Code Runs (Behind the Scenes)

✅ Programmer Writes Code

• The programmer creates a file like Hello.java.

• This file contains Java source code—human-readable instructions.

📁 File Created: Hello.java

🧠 You: Write the code using an editor (like VS Code, IntelliJ, or Notepad).

✅ Compilation using JDK

• The JDK (Java Development Kit) includes a compiler (javac) that converts .java into .class.

🛠️ javac Hello.java → Produces → Hello.class

🔹 .class file contains bytecode, which is platform-independent.

✅ Running the Code using JRE

• You run the code using the java Hello command.

• This sends the .class file (bytecode) to the JRE (Java Runtime Environment).

✅ JRE – What Happens Inside

The JRE contains:

🔸 JVM (Java Virtual Machine):

• It reads the .class bytecode.

• Converts it to machine-specific code (native code).

• This is where the actual execution happens.

🔸 JIT Compiler (Just-In-Time):

• JIT improves performance by converting frequently-used bytecode into machine code just in time for execution.

🔸 Built-in Libraries:

• JRE also includes core Java libraries (.class files, APIs) required during execution.

✅ Execution on the Computer

• The JVM executes the machine code on your computer hardware (CPU, memory).

• Finally, you see the output on your screen.

⚠️ Common Output Issue

If you see nothing or an error:

• Check that the file name matches the class name.

• Make sure the main method is spelled exactly like:

public static void main(String[] args)