What is the difference between using class instances and class methods in PHP?

When using class instances in PHP, you are creating objects of a class that can hold unique data and have their own behavior. Class methods, on the other hand, are functions that are associated with a class and can be called without creating an instance of the class. Class instances are used when you need to work with specific objects and their individual properties, while class methods are useful for defining behavior that is shared among all instances of a class.

// Class definition with class instances
class Person {
    public $name;

    function __construct($name) {
        $this->name = $name;
    }

    function greet() {
        echo "Hello, my name is " . $this->name;
    }
}

$person1 = new Person("Alice");
$person1->greet();

// Class definition with class methods
class Math {
    public static function add($a, $b) {
        return $a + $b;
    }
}

echo Math::add(2, 3);