Overview, Syntax, and Comments

Overview, 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.

Syntax

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

	
    public class Main {
        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:

  • The code that was run lives inside main()
  • Printing to the console used built-in code from System to do so.

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. Your indentation could be a disaster but the code will run the same.

Comments

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

You can leave a comment spanning multiple lines like this:

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

In both cases, compiling and running your code will result in this:

	
    Hello World!
	

That just about does it for a very basic overview of Java, its syntax and how to leave comments!