Advanced Object Oriented Programming
With the addition of capabilities anticipated in a fully object-oriented language, PHP 5 significantly overhauled its object-oriented approach in comparison to earlier iterations. Visibility, abstract and final classes/methods, interfaces, cloning, type-hinting, and other features are all included in this upgraded paradigm. Later chapters of various sources address advanced OOP principles and design patterns, which build upon the foundations of basic syntax and objects.
Abstract Classes and Interfaces
Abstract Classes: PHP 5 added the ability to create abstract classes. They have both practical and intellectual components. Class inheritance can be organised with the aid of abstract classes. Abstract methods methods declared without an implementation may be included in them. By distinguishing a function within a class, abstract is referred to as a “fancy way” to enable a function to be called by numerous sources for a single purpose, hence preventing code duplication. Abstract classes enable child classes to specify methods. The use of abstract classes and methods as OOP design tools is discussed. They can give PHP more flexibility in expressing types and abstractions, however they are not necessarily required.
Interfaces: Classes are required to implement a contract defined by an interface. Interfaces can enhance class type hints and clarify design. Although they are not necessarily required in PHP, interfaces can aid in the expression of types and abstractions, much like abstract classes. Although they do not permit inheriting code implementation like classes do, they do permit a class to implement numerous behaviours. A class must implement the methods listed in the interface if it implements one; else, a fatal error will occur. Interfaces and traits combine to offer a way to design and reuse code. The interface constructs in Java and PHP 5 are contrasted in the sources.
Traits
A way to reuse code outside of a conventional class structure is through traits. They are said to be a means of obtaining the advantages of multiple inheritance without the discomfort that comes with it. Developers can put together functionality that can be utilised in other classes by using traits. In an inheritance tree, this enables you to share functionality between classes that do not (and should not) have a common ancestor. Multiple features can be combined into a class, and traits can even inherit from one another.
For code reuse, traits are regarded as a great collection of building pieces. By enabling code to be inherited from numerous sources, they close the gap left by PHP’s single inheritance model, which states that a class can only extend one parent. Directly declared class methods take precedence over trait methods, and trait methods can override inherited methods.
Polymorphism
In OOP, polymorphism is seen as a crucial idea. It is defined as the capacity to construct several versions from a single parent class or to use the same function or method for various purposes. Writing robust and extensible code with fewer conditional (if()) statements is made easier by using polymorphism, which also helps to represent real-life scenarios and promotes project growth through code reuse (typically via inheritance). The “centre of OOP” is said to be polymorphism and the use of a base class. Code created to function with a general type (parent class or interface) can act on any specific type (subclass or implementing class) type hinting using base classes or interfaces.
Object Inheritance in detail
One of the core ideas in OOP is inheritance. Declaring that a new class is similar to an existing class but has some new or modified attributes and methods is one way to define it. A class can automatically access another class’s features using this process.
- Terminology: The superclass, parent, or base class is the original class from which the inheritance is derived. A “subclass,” “child class,” or “derived class” inherits. Use parent in PHP to refer to the parent class inside the child class.
- Mechanism: In PHP, a class uses the extends keyword in its declaration to inherit from a parent class definition. All of the parent class’s non-private properties and methods are then accessible to the child class.
- Single Inheritance: PHP allows for single inheritance, which means that a class can only inherit from one base class. To overcome this restriction, the idea of traits was presented as a way to reuse code in a manner akin to multiple inheritance.
- Code Reuse: One type of code reuse is inheritance. Rather than being copied, the base class’s code is reused. The derived class immediately inherits any enhancements or changes made to the original class.
- Overriding: By redeclaring inherited methods and properties with the same name, the child class can override them.
- Preventing Overriding/Inheritance: The last keyword can be used to stop a class from being extended at all or to stop a child class from overriding a method.
- Visibility: Properties and methods’ visibility within the inheritance tree is managed by access modifiers (public, protected, and private).
- Design considerations: In contemporary OOP design, composition is frequently preferred over inheritance, and while inheritance is a useful tool for code reuse, it can occasionally be viewed as a bad design decision when it comes to generating subclasses.
Scope Resolution Operator (::)
The “Paamayim Nekudotayim” (Hebrew for “double colon”), or scope resolution operator (::), allows class static members (properties and methods) and constants to be accessed without instantiating the class. It can also be used in child classes to refer to a parent class’s overridden methods or static properties as parent::propertyName or parent::methodName(). For instance, the Math class’s class constant pi is accessed via Math::pi.
Here’s how you access static properties, static methods, and constants from outside the class:
<?php
class MyClass {
// Static property
public static $staticProperty = "This is a static property";
// Class constant
const CLASS_CONSTANT = "This is a class constant";
// Static method
public static function staticMethod() {
return "This is a static method";
}
}
// Accessing static property using ::
echo MyClass::$staticProperty; // Output: This is a static property
echo "<br>";
// Accessing class constant using ::
echo MyClass::CLASS_CONSTANT; // Output: This is a class constant
echo "<br>";
// Calling static method using ::
echo MyClass::staticMethod(); // Output: This is a static method
echo "<br>";
// Example from sources: Accessing a PI constant
class MathValues {
const PI = M_PI;
const PHI = 1.61803;
}
$area = MathValues::PI * $radius * $radius; // Example usage
?>Design Patterns
Some programming issues or patterns recur as software is being designed. Many of these recurrent issues have been handled by the software design community, which has created widely recognised general solutions known as design patterns. Understanding and utilising these patterns has the dual benefits of providing developers with a common vocabulary for software design and saving time by avoiding the need to reinvent solutions. PHP makes it simple to adapt design patterns. Design patterns are divided into three categories by the sources: creational, structural, and behavioural.
- Factory Pattern: This pattern is usually applied when it’s necessary to build a tangible instance of a base class’s subclasses. Typically, a factory class has a static method that takes in some input and determines which particular class instance typically a subclass to construct and return.
- Singleton Pattern: This pattern guarantees that during the course of an application’s operation, only one instance of a specific class may be created. In order to prevent direct calls to the class’s constructor (__construct()) and cloning method (__clone()) using new or clone, this is frequently accomplished by making them private. The only way to obtain the single instance is through the class’s public static function, which is frequently called getInstance(). On the initial call, this method generates the instance, and on all future calls, it returns the same instance.
- MVC: Aspects of PHP programming like as Object Oriented Programming, design patterns, and web techniques like sessions and database interaction are covered in the sources that are provided. However, none of these sites mention MVC.