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Classes and Objects in PHP

Learn how to use object-oriented programming in PHP.

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Key Concepts

Review core concepts you need to learn to master this subject

PHP extends keyword

PHP Constructor Method

PHP class

PHP extends keyword

// Dog class inherits from Pet class. 
class Dog extends Pet {
  function bark() {
    return "woof";
  }
}

In PHP, to define a class that inherits from another, we use the keyword extends:

class ChildClass extends ParentClass {
}

The newly defined class can access members with public and protected visibility from the base class, but cannot access private members.

The newly defined class can also redefine or override class members.

PHP Constructor Method

// Dog class inherits from Pet class. 
class Dog extends Pet {
  function bark() {
    return "woof";
  }
}

A constructor method is one of several magic methods provided by PHP. This method is automatically called when an object is instantiated. A constructor method is defined with the special method name __construct. The constructor can be used to initialize an object’s properties.

PHP class

// Dog class inherits from Pet class. 
class Dog extends Pet {
  function bark() {
    return "woof";
  }
}

In PHP, classes are defined using the class keyword.

Functions defined within a class become methods and variables within the class are considered properties.

There are three levels of visibility for class members:

public (default) - accessible from outside of the class
protected - only accessible within the class or its descendants
private - only accessible within the defining class

Members can be defined to be static:

Static members are accessed using the Scope Resolution Operator (::)

Classes are instantiated into objects using the new keyword. Members of an object are accessed using the Object Operator (->).

Classes and Objects

Lesson 1 of 1

1
In our PHP programs so far, we’ve relied on data types built into the language—we’ve used String, Number and Boolean data types directly and saved data in variables. We’ve also used Arrays to organ…
2
In the previous exercise, we asked you to imagine a class for pets. Let’s see how we would actually create a PHP Pet class. To define a Pet class, we use the class keyword followed by the class n…
3
In the previous exercise, we created a class (a blueprint) for any pet we may want to make. But we didn’t make any actual, individual pet objects. Since objects are specific instances of a class, t…
4
In addition to properties, we can define class methods – essentially functions each object will contain. Methods are frequently used to interact with an object’s properties in a defined manner. M…
5
A constructor method is one of several magic methods provided by PHP. This method is automatically called when an object is instantiated. A…
6
Imagine we wanted a Dog class in our program. This class would have all the properties of the more general Pet class, but it would have a few more properties and methods specific to only dogs. Rath…
7
Sometimes, we want to change how methods behave for subclasses from the original parent definition. This is called overloading a method. To do this, define a new method within the subclass with t…
8
To understand visibility we need to think about how classes will be used in complex programs—in large applications, a class might be used in diverse situations (passed around inside functions and u…
9
A class’s private members can only be accessed using methods within that class itself. This isn’t usually the desired effect when we have subclasses. For example, the following code will throw …
10
The concept of only accessing properties through methods is commonly referred to as using getters and setters. For example: class Pet { private $name; function setName($name) { $this->…
11
Instantiating objects is the most common way to use classes and is also the most in-line with OOP principles. Sometimes though, it can be useful to group a set of utility functions and variables to…
12
Now you have the knowledge to create your own classes and objects in PHP using OOP! Take some time to review the concepts before moving on: - Classes are defined using the class keyword. - Function…