• Table of Content

Hello, World

Before writing any Java code, let’s understand some basic building blocks of Java.

Building Blocks

• Functions / Methods

  Functions are the basic building blocks of a Java program. A function is a snippet of code that performs a specific task. Every function has a return type and a set of parameters which are optional. Every Java program must have a main method. Functions belonging to a class are called as methods.

• Class

  A class is a container for a set of related functions. No method can exists without a class. A class is more than that which will be discussed later

• Package —

  A package is a collection of related classes. The standard practice for the base package name is the domain name in reverse. We don’t actually need a domain on the internet. It is just a way to create a namespace for the project.

Hello World — The First Program

package io.rizwan; // <----- package name

public class Main { // <-------- class declaration
	public static void main(String[] args) { // <------- method declaration
		 // print "Hello World" on the console
	   System.out.println("Hello World");
	}
}

System.out.println("Hello World"); is used to print any string that is passed as an argument on the console.

Detailed Explanation —

1. The System is a class that has a field called out which returns a reference, of type PrintStream. The PrintStream class has a method called println which prints the text that is passed as an argument on the new line in the console or terminal.
2. A String is a sequence of characters in “double quotes”. A String “Hello World” is passed as an argument in the println method
3. Comments are statements that are written to help other developers understand the code. Single-line comments are prefixed by // (Double forward slashes). Comments don’t get executed. As a best practice we should comment about why we wrote the block of code instead of what and how.

Naming Convention, for Classes — PascalNamingConvention and for Methods — camelNamingConvention. Also, Starting curly braces should be on the same line as the method declaration.

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Every statement in Java ends with a semicolon. Java is a case-sensitive language i.e. println and Println will be treated differently. In fact the program won’t compile if we write Println

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Variables