What Is a Constructor?

This section describes what is a constructor - a special method to be invoked automatically when a new object is created from a class. The main purpose of the constructor is to provide initial values to object properties.

What Is a Constructor? A constructor is a special method to be invoked automatically when a new object is created from a class. The main purpose of the constructor is to provide initial values to object properties.

In PHP, the constructor method must be named as "__construct()". For example, the following class provides a constructor to initialize two properties of the new object:

<?php /* MyMessage.php
 - Copyright (c) 2015, HerongYang.com, All Rights Reserved.
*/

class MyMessage {
   public $text;
   public $length;

   function __construct($t) {
      $this->text = $t;
      $this->length = strlen($t);
   }
   public function show() {
      echo $this->text . "\n";
      echo "Number of bytes in the message: " . $this->length . "\n";
   }
}

   $msg = new MyMessage("Hello there!");
   $msg->show();
?>

Notice that:

If you run the above tutorial example, you will get:

Hello there!
Number of bytes in the message: 12

Last update: 2015.

Table of Contents

 About This Book

 Introduction and Installation of PHP 7.0

 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

 Configuring and Sending out Emails

 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

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

 Outdated Tutorials

 References

 PDF Printing Version