Hello, World!

“Hello, World!” is the name of a simple program that outputs Hello, World! On the screen. Since it’s very simple, it’s often used to introduce a programming language to new programmers.

Let’s explore how a Java “Hello, World!” program works:

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

Let’s go through this line by line:

1. public class Main { [...] }
   • In Java, every file contains one main class that has the same name as the file its in (in this case the above file would be called Main.java). We’ll talk about classes more in the future, but for now think of them as a container for parts of our code. Code between the opening and closing curly parenthesis is considered “part” of that class.
2. public static void main(String[] args) { [...] }
   • This is the main method Every application in Java contains a main method. When we run our program, the java compiler starts running our code from here.
3. System.out.println("hello World");
   • This is known as a print statement. It prints the text “Hello, World!” to standard output (your screen). The text inside the quotation marks is called a String in Java. We use System.out.println(" [...] ") to print the text inside the double quotes to the screen.

How does the main method work? Good question. However, we will not discuss it in this article. After all, it’s a basic program to introduce the Java programming language to you! We will learn the meaning of keywords like public, static, void, and how methods work in later chapters.

In Java, every application begins with a class definition. In the above program, Main is the name of the class, and is defined on the first line. We’ll talk about classes more in the future, but for now think of them as a container for different parts of our code.

All the content in this section (excluding functions) can be thought of as running inside the above “hello world” example (even if the code examples don’t explicitly state it)

Comments

Comments are intended for users reading our code to understand its purpose & functionality. They are completely ignored by the Java compiler.

There are 2 ways to create comments in Java:

1. Using // for single-line comments

   • // Hello! This is a single-line comment and is great for short explanations of code.
     

2. Using /* ... */ for multi-line comments

   • /* Hi! This is a comment that spans across
       multiple lines
       great for giving deeper explanations on why or how our code works.
     

Code snippets throughout this guide may use comments to provide further context or explain what’s going on.