PHP Classes

Table of Contents

• Introduction
• Defining a Class
• Initializing Properties and Calling Methods

Introduction

Before you can use an object, you must define a class with the class keyword. Class definitions contain the class name (which is case-sensitive), its properties, and its methods.

Defining a Class

Syntax

 1<?php
 2    class className // class name
 3    {
 4        public $property_1, $property_2; // properties
 5
 6        function method_1() //method
 7        {
 8            statement(s);
 9        }
10    }
11?>

In the above class definition, we defined a class with the class keyword. The name of the class is className (which is case-sensitive). We also include two properties ($property_1 and $property_2) using the public keyword. More on the public keyword later. Let’s take a look at an example first.

Example

 1<?php
 2    $object = new User;
 3    print_r($object);
 4
 5    class User
 6    {
 7        public $name, $age;
 8
 9        function say_something()
10        {
11        echo "Method statements go here";
12        }
13    }
14?>

User Object ( [name] => [age] => )

In the above example, we define the class User with two properties $name and $age. We also create a new instance (called $object) of the class. I have also used print_r to display $object. Note that echo will not be able to display objects.

In the above output, we see that both properties $name and $age are not initialized yet.

Initializing Properties and Calling Methods

In the following example, we have the same User class defined above. After creating an instance of the class called $object, we also initialize its two properties using the syntax $object->property = value, taking note that the $ is left out from the property name. The -> character pair is called the object operator and we use it to access an object’s properties and methods.

We also call the object’s method using a similar syntax $object->method().

Example

 1<?php
 2    $object = new User;
 3    print_r($object);
 4
 5    echo "<br>";
 6
 7    $object->name = "Julian"; // initialize object's name property
 8    $object->age = "32"; // initialize object's age property
 9    print_r($object);
10
11    echo "<br>";
12
13    $object->say_something(); // calling object's method
14
15
16    class User
17    {
18        public $name, $age;
19
20        function say_something()
21        {
22        echo "Method statements go here.";
23        }
24    }
25?>

User Object ( [name] => [age] => )
User Object ( [name] => Julian [age] => 32 )
Method statements go here.

In the above example, we placed the class definition at the end of the script. Note that after initialization, the values of both properties are displayed: User Object ( [name] => Julian [age] => 32 ).