Java Basics

This chapter introduces the fundamental building blocks of the Java language, providing a foundation for writing your first programs.

Basic Syntax

At the core of every Java program is a class. The execution of a program begins in the main method, which serves as the entry point. It is important to be mindful of Java's syntax rules. The language is case-sensitive, meaning that myVariable and MyVariable would be treated as two distinct variables. By convention, class names should always begin with an uppercase letter, while method names should start with a lowercase letter.

Check out the Java naming convention to learn how to properly name things in Java.

"Hello, World!" Example

The simplest program you can write in Java is the classic "Hello, World!". This program's sole purpose is to print the phrase "Hello, World!" to the console.

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

Let's break down this example:

• The line public class HelloWorld declares a class named HelloWorld, and the file containing this code must be saved as HelloWorld.java.
• The main method, declared as public static void main(String[] args), is where the program's execution starts.
• The statement System.out.println("Hello, World!"); is responsible for printing the text to the console.
• The lines starting with // are single-line comments, which are ignored by the compiler.

Java Comments

Comments are essential for explaining code and improving its readability. The Java compiler ignores them entirely.

There are three types of comments in Java. Single-line comments start with //. Multi-line comments begin with /* and end with */. Finally, Javadoc comments, which start with /** and end with */, are used to generate documentation for your code.

// This is a single-line comment.

/*
This is a
multi-line
comment.
*/

/**
 * This is a Javadoc comment, used for generating documentation.
 */