Java Syntax

In the previous chapter, we created a Java file called Main.java, and we used the following code to print "Hello World" to the screen:

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

Example Explained

Every line of code that runs in Java must be inside a class. The class name should always start with an uppercase first letter. In our example, we named the class Main.

Note: Java is case-sensitive: MyClass and myclass have different meanings.

The name of the Java file must match the class name. When saving the file, save it using the class name and add .java to the end of the filename. To run the example above on your computer, ensure that Java is properly installed. Refer to the Get Started chapter for installation instructions. The output should be:

Hello World

The main Method

The main() method is required and appears in every Java program:

public static void main(String[] args)

Any code inside the main() method will be executed. Don't worry about the keywords before and after it—you will learn them gradually.

For now, just remember that every Java program has a class name that must match the filename, and every program must contain the main() method.

System.out.println()

Inside the main() method, we can use the println() method to print a line of text to the screen:

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

Note: The curly braces {} mark the beginning and the end of a block of code.

System is a built-in Java class that contains useful members, such as out, which stands for "output". The println() method, short for "print line", is used to print a value to the screen (or a file).

Don't worry too much about how System, out, and println() work. Just know that you need them together to print output to the screen.

You should also note that each code statement must end with a semicolon (;).