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What are the four core principles of object oriented programming, and how does PHP support each of them? What are the three visibility modifiers in PHP, public, protected, and private, and how do they control access to a class's properties and methods? How does inheritance work in PHP using the extends keyword, and how do you call a parent class's constructor or method from within a child class? How does the readonly property modifier introduced in PHP 8.1 help enforce immutability for specific class properties? How does PHP handle multiple inheritance limitations, and how do traits provide a mechanism for sharing reusable code across multiple unrelated class hierarchies? How does late static binding, using the static keyword instead of self, allow inherited static methods to correctly reference the actual calling child class rather than the parent class where the method was originally defined?
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What is the difference between a static property or method and an instance property or method in PHP?

Intermediate

Answer

A static property or method belongs to the class itself rather than to any specific instance, meaning it is accessed using the class name and scope resolution operator rather than through an object instance, and its value is shared across the entire application rather than being unique to each individual object, while an instance property or method requires creating an actual object and each instance maintains its own independent copy of instance property values.
class Counter {
    private static int $count = 0;
    public static function increment(): void {
        self::$count++;
    }
}
Counter::increment();
Real-world example A utility class tracking how many database queries have been executed throughout the entire request uses a static property, since that count needs to be shared globally rather than tracked separately per individual object instance.

Common follow-ups: When is it appropriate to use a static method instead of an instance method?;Can a static method access instance properties or call instance methods?

Functions & Scope;Design Patterns in PHP
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