PHP Class Constructor

In this chapter you will learn:

1. What is a constructor
2. Syntax to create a constructor
3. Example - Class with a constructor
4. Example - Constructor with arguments
5. Example - Parent Constructors

Definition

A constructor is a special method that is called by PHP when you create an instance of the class.

Syntax

PHP class constructor has the following syntax.

Example 1

<?PHP// jav a  2s . c o m
   class MyClass { 
     function __construct() { 
       echo "I am being constructed."; 
     } 
   } 
          
   $obj = new MyClass;  
?>

The code above generates the following result.

The class, MyClass , contains a very simple constructor that just displays the message. When the code then creates an object from that class, the constructor is called and the message is displayed.

Example 2

You can pass arguments to constructors, like normal methods.

<?PHP/*from  j  ava2s  .  c o  m*/
   class Person { 
     private $_firstName; 
     private $_lastName; 
     private $_age; 
          
     public function __construct( $firstName, $lastName, $age ) { 
       $this-> _firstName = $firstName; 
       $this-> _lastName = $lastName; 
       $this-> _age = $age; 
     } 
   } 
          
   $p = new Person( "James", "Bond", 28 ); 
?>

The Person class contains three private properties and a constructor that accepts three values, setting the three properties to those values.

Example 3

If a class contains a constructor, it is only called if objects are created from that class.

If an object is created from a child class, only the child class's constructor is called.

To make a child class call its parent's constructor call parent::__construct().

<?PHP/*from ja v  a2  s  .c om*/
class NameTag {
       public $Words;
}

class Book {
       public $Name;

       public function say() {
               print "Woof!\n";
       }

       public function __construct($BookName) {
               print "Creating a Book: $BookName\n";
               $this->Name = $BookName;
       }
}


class ComputerBook extends Book {
       public function say() {
               print "Computer!\n";
       }

       public function __construct($BookName) {
               parent::__construct($BookName);
               print "Creating a computer book\n";
       }
}
?>

It is better to call parent::__construct() first from the constructor of a child class, in order to set up all the parent's properties.

Next chapter...

What you will learn in the next chapter:

1. What are PHP Class Destructors
2. Syntax for Class Destructors
3. Example - Call __destruct()
4. Call parent::__destruct().
5. Deleting Objects

Concept for Object Oriented Design

PHP Class Definition

PHP Create Object from Class

PHP Class Properties

PHP Iterating Object Properties

PHP Class Inheritance

PHP Overriding Methods

PHP final Classes and Methods

PHP Abstract Class

PHP Class Access Control Modifiers

PHP Class Constructor

PHP Class Destructors

PHP Class Magic Methods