How to Compile and Run a Java Program Using Command Line

• Compiling and running Java programs from the command line helps you understand how Java works internally and is essential for interviews, debugging, and real-world development.

Prerequisites

• Java JDK installed

Steps to follow
Step 1: Create a Java Program

• Create a file named HelloWorld.java

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

Important: The file name must match the class name.

Step 2: Open Command Prompt / Terminal

• Navigate to the folder where the .java file is saved.
• Type cmd on the path bar

-Command prompt gets opened

Step 3: Compile the Java Program

• Use the javac compiler:

javac HelloWorld.java

What Happens Internally?

• javac checks syntax
• Converts source code into bytecode
• Generates a file: HelloWorld.class

Step 4: Run the Java Program

Use the java command (without .class):

java HelloWorld

Output:

Hello, Java!

*Compilation Flow *

• .java file → Source code
• javac → Bytecode (.class)
• java → JVM loads and executes bytecode