What Is a Static Variable

This section describes what is a static variable - a special variable declared at the class level to be shared by all objects of the class.

What Is a Static Variable? A static variable is a special variable declared at the class level to be shared by all objects of the class.

In PHP, a static variable is declared with the keyword "static" and invoked with the "::" operator with the class name. For example, the following tutorial example provides a class with a static variable called $count:

/* MyPassGenerator.php
#- Copyright (c) 2015-2019, HerongYang.com, All Rights Reserved.

class MyPassGenerator {
   public static $count = 0;
   public $sequence;
   private $password;

   public function __construct() {
      self::$count += 1;
      $this->sequence = self::$count;
      $words = array_merge(range('a', 'z'), range('A', 'Z'));
      $this->password = substr(implode($words), 0, 6);
   public function getPass() {
      return $this->password;

  $first = new MyPassGenerator();
  $second = new MyPassGenerator();
  echo "Total # of objects: ". MyPassGenerator::$count ."\n";
  echo "First object: \n";
  echo "   Sequence: " . $first->sequence ."\n";
  echo "   Password: " . $first->getPass() ."\n";
  echo "Second object: \n";
  echo "   Sequence: " . $second->sequence ."\n";
  echo "   Password: " . $second->getPass() ."\n";

Notice that "self" is used as a keyword to represent the current class.

If you run the above tutorial example, you will get something like this:

C:\herong> \php\php MyPassGenerator.php

Total # of objects: 2
First object:
   Sequence: 1
   Password: BOYXpv
Second object:
   Sequence: 2
   Password: KRzZOS

Last update: 2019.

Table of Contents

 About This Book

 Introduction and Installation of PHP 7.3

 PHP Script File Syntax

 PHP Data Types and Data Literals

 Variables, References, and Constants

 Expressions, Operations and Type Conversions

 Conditional Statements - "if" and "switch"

 Loop Statements - "while", "for", and "do ... while"

 Function Declaration, Arguments, and Return Values

 Arrays - Ordered Maps

Introduction of Class and Object

 What Is a Class

 What Is an Object

 What Is a Constructor

 What Is a Static Method

What Is a Static Variable

 What Is a Superclass and a Subclass

 What Is an Abstract Class

 What Is an Abstract Method

 What Is an Interface

 What Is a Trait

 What Is an Overloaded Property

 What Is an Overloaded Method

 What Is Object Property Iteration

 What Is Object Cloning

 What Is Object Serialization

 What Is in an Object Variable

 Updating Variables Who Share an Object

 Passing Objects as Function Arguments

 Integrating PHP with Apache Web Server

 Retrieving Information from HTTP Requests

 Creating and Managing Sessions in PHP Scripts

 Sending and Receiving Cookies in PHP Scripts

 Controlling HTTP Response Header Lines in PHP Scripts

 MySQL Server Connection and Access Functions

 Functions to Manage Directories, Files and Images

 SOAP Extension Function and Calling Web Services

 SOAP Server Functions and Examples

 Localization Overview of Web Applications

 Using Non-ASCII Characters in HTML Documents

 Using Non-ASCII Characters as PHP Script String Literals

 Receiving Non-ASCII Characters from Input Forms

 "mbstring" Extension and Non-ASCII Encoding Management

 Managing Non-ASCII Character Strings with MySQL Servers

 Configuring and Sending out Emails

 Outdated Tutorials


 Full Version in PDF/EPUB