Lesson 3: Your First Java Program: 'Hello World' Explained

Let's write the canonical first program.

The Code

Create a file named HelloWorld.java:

java public class HelloWorld { public static void main(String[] args) { // This line prints the message to the console System.out.println("Hello, World!"); } }

Deconstructing the Code

Term	Description
`public`	An access modifier. It means this class/method is accessible from everywhere.
`class`	Keyword used to define a class. The class name must match the filename (`HelloWorld`).
`static`	Allows the `main` method to be called without creating an instance of the class.
`void`	Specifies that the method does not return any value.
`main`	The entry point for the execution of any Java application. The JVM starts here.
`String[] args`	An array of strings used to pass command-line arguments to the application.
`System.out.println()`	A standard method used to output text to the console (standard output).

Execution (Command Line)

Compile: Turns your .java source code into platform-independent bytecode (.class file). bash javac HelloWorld.java
Run: Executes the bytecode using the JVM. bash java HelloWorld

Output:

Hello, World!