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Java Syntax


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");
  }
}

Try it Yourself »

Example explained

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

Note: Java is case-sensitive: "MyClass" and "myclass" has different meaning.

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, make sure that Java is properly installed: Go to the Get Started Chapter for how to install Java. The output should be:

Hello World

The main Method

The main() method is required and you will see it 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 main. You will get to know them bit by bit while reading this tutorial.

For now, just remember that every Java program has a class name which must match the filename, and that 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");
}

Try it Yourself »

Note: The curly braces {} marks 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 is short 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 System, out and println(). Just know that you need them together to print stuff to the screen.

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


Test Yourself With Exercises

Exercise:

Insert the missing part of the code below to output "Hello World".

public class MyClass {
  public static void main(String[] args) {
    ..("Hello World");
  }
}

Start the Exercise