Overview of Java Syntax and Comments

Java is an object-oriented programming language. What this means is that basically everything is an object. We'll learn more about what an object is and why it's important later in this class.

Let's look at how we printed Hello World! again:

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

There's definitely a lot going on here, however for the purposes of this class, there's only a few things you need to take away from this for now:

• This code defines the main() method, which is the starting point for any Java program.
• When you run this code, the JVM(Java Virtual Machine) calls the main() method and executes its contents.
• The line System.out.println("Hello World!"); prints the message "Hello World!" to the console, demonstrating basic output functionality.
• When it comes to the syntax, every line of code in Java must end in a semicolon. Unlike some programming languages like Python, indentation doesn't matter here.

Comments in Java

Comments are useful in programming languages to leave yourself or another developer a note of some kind. This is also called documenting your code. Comments are entirely ignored by the compiler so they do not affect the execution or performance of your code.

Here's how a single-line comment looks like:

public class HelloWorld {
    public static void main(String[] args) {
        // this is a single-line comment!
        System.out.println("Hello World!");
    }
}

You can leave a comment spanning multiple lines like this:

public class HelloWorld {
    public static void main(String[] args) {
        /* this is a
           multi-line comment!
          */
        System.out.println("Hello World!");
    }
}