What Is an Abstract Class

This section describes what is an abstract class - a class whose definition is considered to be not fully completed and is required to be extended into subclasses to complete the definition. No objects are allowed to be created from an abstract class directly.

What Is an Abstract Class? An abstract class is a class whose definition is considered to be not fully completed and is required to be extended into subclasses to complete the definition. No objects are allowed to be created from an abstract class directly.

In PHP, an abstract class is declared with the keyword "abstract". For example, the following tutorial example provides an abstract class MyShape which is extended by subclass MyCircle.

<?php
/* MyCircle.php
#- Copyright (c) HerongYang.com. All Rights Reserved.
*/

abstract class MyShape {
   public $x;
   public $y;
   public $type;

   public function __construct($x,$y,$t) {
      $this->x = $x;
      $this->y = $y;
      $this->type = $t;
   }
   public function showType() {
     echo "   Type: " . $this->type ."\n";
   }
   public function showCenter() {
     echo "   Center: " . $this->x .", " . $this->y ."\n";
   }
}

class MyCircle extends MyShape {
   public $radius;

   public function __construct($x,$y,$r) {
      parent::__construct($x,$y,"Circle");
      $this->radius = $r;
   }
   public function showArea() {
      echo "   Area: " . 3.1459*$this->radius**2 ."\n";
   }
}

  $object = new MyCircle(1.0,2.0,0.5);

  echo "MyCircle object: \n";
  $object->showType();
  $object->showCenter();
  $object->showArea();
?>

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

C:\herong> \php\php MyCircle.php

MyCircle object:
   Type: Circle
   Center: 1, 2
   Area: 0.786475

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

 Interface with Operating System

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

 Managing File Upload

 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

 Parsing and Managing HTML Documents

 Configuring and Sending out Emails

 Image and Picture Processing

 Managing ZIP Archive Files

 Managing PHP Engine and Modules on macOS

 Managing PHP Engine and Modules on CentOS

 Outdated Tutorials

 References

 Full Version in PDF/EPUB