Hello World in Java

Every programming journey starts with Hello World. Let’s write our first Java program.

The Code

Create a file named HelloWorld.java:

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

Understanding the Code

• public class HelloWorld - Defines a public class. In Java, the filename must match the class name.
• public static void main(String[] args) - The entry point of every Java application.
• System.out.println() - Prints text to the console followed by a newline.

Running with Docker

The easiest way to run this without installing Java locally:

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# Pull the official Eclipse Temurin JDK image
docker pull eclipse-temurin:21-jdk

# Run the program
docker run --rm -v $(pwd):/app -w /app eclipse-temurin:21-jdk \
    sh -c "javac HelloWorld.java && java HelloWorld"

Running Locally

If you have Java installed (JDK 11+):

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# Compile
javac HelloWorld.java

# Run
java HelloWorld

Expected Output

Hello, World!

Key Concepts

1. Java is compiled - Source code (.java) is compiled to bytecode (.class)
2. Bytecode runs on the JVM - Java Virtual Machine executes the bytecode
3. Class names matter - The filename must match the public class name
4. main() is special - This is where program execution begins