PHP Classes/Objects

PHP Classes & Objects: Instantiation, Properties, & Methods

A class is a blueprint/template that defines the properties and methods common to all objects created from it. An object is an instantiated instance of a class stored in memory.

Class Component Anatomy

class Car // Class Name
{
    // 1. Property (State)
    public string $brand;

    // 2. Method (Behavior)
    public function startEngine(): string
    {
        return "Engine started!";
    }
}

// 3. Object Instantiation
$myCar = new Car();

Class to Object Relationship

flowchart TD
    A["Class Blueprint (Car)"] -->|new Car()| B["Instance Object 1 ($tesla)"]
    A -->|new Car()| C["Instance Object 2 ($bmw)"]
    B --> B1["$tesla->brand = 'Tesla'"]
    C --> C1["$bmw->brand = 'BMW'"]

Practical Code Example

<?php
declare(strict_types=1);

class Product
{
    // Typed Properties
    public string $name;
    public float $price;
    public int $stockQuantity = 0;

    // Method utilizing internal properties via $this
    public function getFormattedPrice(): string
    {
        return "$" . number_format($this->price, 2);
    }

    public function isInStock(): bool
    {
        return $this->stockQuantity > 0;
    }
}

// Instantiating multiple independent objects
$laptop = new Product();
$laptop->name = "Developer Laptop";
$laptop->price = 1499.99;
$laptop->stockQuantity = 5;

$mouse = new Product();
$mouse->name = "Wireless Mouse";
$mouse->price = 29.99;
$mouse->stockQuantity = 0;

echo "Item 1: {$laptop->name} | Price: {$laptop->getFormattedPrice()} | In Stock?: " . ($laptop->isInStock() ? "Yes" : "No") . "
";
echo "Item 2: {$mouse->name} | Price: {$mouse->getFormattedPrice()} | In Stock?: " . ($mouse->isInStock() ? "Yes" : "No") . "
";

Best Practices

• Use UpperCamelCase for Class Names: Follow PSR-12 conventions (ProductService, UserAccount).
• Use $this-> to Access Instance Members: Always reference instance properties and methods using $this->propertyName inside class methods.
• Type-Hint Class Properties: Declare property scalar types (public string $name;) to prevent type assignment errors.

Self-Check Challenge

Write a class Book with properties string $title and float $price, and instantiate an object $myBook = new Book();!