PHP Tutorials - Herong's Tutorial Examples - v5.17, by Herong Yang
What Is a Superclass and a Subclass
This section describes what is a Superclass and a Subclass - a pair of classes that the second class extends from the first class. An object of subclass inherits all properties and operations from the superclass.
What Is a Superclass and a Subclass? A superclass and a subclass is a pair of classes that the second class extends from the first class. An object of subclass inherits all properties and operations from the superclass.
In PHP, a subclass is declared with the keyword "extends" followed by the superclass name. For example, the following tutorial example provides a class MySquare which is extended from class MyRectangle. In this case, MyRectangle is the superclass and MySquare is subclass.
<?php
/* MySquare.php
#- Copyright 2015 (c) HerongYang.com. All Rights Reserved.
*/
class MyRectangle {
public $width;
public $height;
public function __construct($w,$h) {
$this->width = $w;
$this->height = $h;
}
public function getArea() {
return $this->width * $this->height;
}
}
class MySquare extends MyRectangle {
public $length;
public function __construct($l) {
parent::__construct($l,$l);
$this->length = $l;
}
public function getArea() {
return $this->length**2;
}
}
$object = new MySquare(2.0);
echo "MySquare object: \n";
echo " Class name: ". get_class($object) ."\n";
echo " Length: " . $object->length ."\n";
echo " Width: " . $object->width ."\n";
echo " Height: " . $object->height ."\n";
echo " Area: " . $object->getArea() ."\n";
echo " Is subclass of MyRectangle: "
. is_subclass_of($object, 'MyRectangle') ."\n";
echo " Is subclass of MySquare: "
. is_subclass_of($object, 'MySquare') ."\n";
?>
Notice that:
If you run the above tutorial example, you will get something like this:
herong> \php\php MySquare.php MySquare object: Class name: MySquare Length: 2 Width: 2 Height: 2 Area: 4 Is subclass of MyRectangle: 1 Is subclass of MySquare:
Table of Contents
Introduction and Installation of PHP
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
Interface with Operating System
►Introduction of Class and Object
►What Is a Superclass and a Subclass
What Is an Overloaded Property
What Is Object Property Iteration
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
Parsing and Managing HTML Documents
Configuring and Sending Out Emails
Managing PHP Engine and Modules on macOS