Basic Structure of a Java Program

The first thing to know about Java is that source files have a .java extension. Java follows Pascal Case for file names, where each word in the name is capitalized (e.g., HelloWorld). Java is case-sensitive, meaning that HelloWorld and Helloworld are considered different class names.

Your Java program must begin with a class definition, where the class name matches the file name.

public class HelloWorld {
    ...
}

In this example, public class HelloWorld defines a class named HelloWorld, saved in a file called HelloWorld.java. In Java, all code resides within a class.

Next, you need to add the main method inside the class to run your program’s code. For this tutorial series, it’s important to remember the main method’s signature: public static void main(String[] args). As you learn more about Java’s object-oriented programming concepts, you’ll gain a clearer understanding of each keyword.

public class HelloWorld {
    
    public static void main(String[] args) {
        ...
    }
}

Within the main method, you’ll write statements that determine your program’s actions. Here, System.out.println() is used to print Hello, World! to the console.

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

Simple enough? We hope it is.

In the following tutorials, we’ll use the template shown below for our code examples.

public class Main {
    
    public static void main(String[] args) {
        ...
    }
}