1.1 Your First Java Program

The classic first program when introducing any new language is Hello World, or a program that prints Hello World to the console. In Java, Hello World can be written as such:

void main() {
    IO.println("Hello world!");
}

Compare this with the Python equivalent:

print("hello world!")

Compared to the extreme simplicity of Python, we observe the following features of this simplest Java program:

• The main function: all the code that runs must be inside of a function called main. We'll cover what the void means later.

• Curly braces {} enclose sections of code (functions, classes, and other types of code that will be covered in future chapters).

• All statements must end with a semi-colon.

• Printing requires us to use dot notation, going to some library called IO and asking for its print function.

For fun, see Hello world! in other languages.