Understanding Classes, Objects, and OOP Principles in PHP

Class Definition and Example

In PHP, a class defines a template for objects, specifying properties and methods. The following example defines a simple Dog class with $name and $breed properties and bark() and fetch() methods.

<code>&lt;?php<br/>class Dog {<br/>    public $name;<br/>    public $breed;<br/><br/>    public function bark() {<br/>        echo "Woof! Woof!";<br/>    }<br/><br/>    public function fetch() {<br/>        echo "{$this->name} is fetching.";<br/>    }<br/>}<br/>?&gt;</code>

Object Characteristics

Objects are concrete instances of a class. The example creates two Dog objects, assigns distinct names and breeds, and calls their methods to demonstrate independent state.

<code>&lt;?php<br/>// Creating objects from the Dog class<br/>$dog1 = new Dog();<br/>$dog2 = new Dog();<br/><br/>// Setting property values<br/>$dog1->name = "Buddy";<br/>$dog1->breed = "Labrador";<br/>$dog2->name = "Max";<br/>$dog2->breed = "Golden Retriever";<br/><br/>// Calling methods<br/>$dog1->bark(); // Outputs: Woof! Woof!<br/>$dog2->fetch(); // Outputs: Max is fetching.<br/>?&gt;</code>

Abstraction

Abstraction hides implementation details behind a common interface. An abstract Shape class declares an abstract calculateArea() method, while concrete Circle and Rectangle subclasses implement the method with specific formulas.

<code>&lt;?php<br/>abstract class Shape {<br/>    abstract public function calculateArea();<br/>}<br/><br/>class Circle extends Shape {<br/>    private $radius;<br/>    public function __construct($radius) {<br/>        $this->radius = $radius;<br/>    }<br/>    public function calculateArea() {<br/>        return pi() * pow($this->radius, 2);<br/>    }<br/>}<br/><br/>class Rectangle extends Shape {<br/>    private $length;<br/>    private $width;<br/>    public function __construct($length, $width) {<br/>        $this->length = $length;<br/>        $this->width = $width;<br/>    }<br/>    public function calculateArea() {<br/>        return $this->length * $this->width;<br/>    }<br/>}<br/><br/>$circle = new Circle(5);<br/>$rectangle = new Rectangle(4, 6);<br/>echo 'Circle Area: ' . $circle->calculateArea() . PHP_EOL;<br/>echo 'Rectangle Area: ' . $rectangle->calculateArea() . PHP_EOL;<br/>?&gt;</code>

Encapsulation

Encapsulation bundles data and behavior, exposing only selected operations. The Car class keeps $model , $color , and $fuelLevel private, providing public getters and a drive() method that safely modifies fuel level.

<code>&lt;?php<br/>class Car {<br/>    private $model;<br/>    private $color;<br/>    private $fuelLevel;<br/><br/>    public function __construct($model, $color) {<br/>        $this->model = $model;<br/>        $this->color = $color;<br/>        $this->fuelLevel = 100;<br/>    }<br/><br/>    public function getModel() { return $this->model; }<br/>    public function getColor() { return $this->color; }<br/>    public function getFuelLevel() { return $this->fuelLevel; }<br/>    public function drive() {<br/>        $this->fuelLevel -= 10;<br/>        if ($this->fuelLevel < 0) { $this->fuelLevel = 0; }<br/>    }<br/>}<br/><br/>$myCar = new Car("Toyota", "Blue");<br/>echo "Model: " . $myCar->getModel() . "<br>";<br/>echo "Color: " . $myCar->getColor() . "<br>";<br/>echo "Fuel Level: " . $myCar->getFuelLevel() . "%<br>";<br/>$myCar->drive();<br/>echo "Updated Fuel Level after driving: " . $myCar->getFuelLevel() . "%";<br/>?&gt;</code>

Inheritance

Inheritance allows a subclass to reuse and extend a parent class. An Animal base class defines a $name property and an eat() method; Dog and Cat subclasses inherit these members and add their own bark() and meow() methods.

<code>&lt;?php<br/>class Animal {<br/>    public $name;<br/>    public function __construct($name) { $this->name = $name; }<br/>    public function eat() { return $this->name . ' is eating.'; }<br/>}<br/><br/>class Dog extends Animal {<br/>    public function bark() { return $this->name . ' is barking.'; }<br/>}<br/><br/>class Cat extends Animal {<br/>    public function meow() { return $this->name . ' is meowing.'; }<br/>}<br/><br/>$dog = new Dog('Buddy');<br/>$cat = new Cat('Whiskers');<br/>echo $dog->eat();<br/>echo $dog->bark();<br/>echo $cat->eat();<br/>echo $cat->meow();<br/>?&gt;</code>