In PHP object oriented programming, what is the difference between accessing a class method using -> and accessing it using :: ?

Introduction / Context:
This question tests understanding of two important PHP operators that appear frequently in object oriented code, namely the object operator -> and the scope resolution operator ::. Knowing when to use each operator is essential when you work with instance members, static members, and class constants. Interviewers often ask this to confirm that a candidate understands the difference between object context and class context in PHP.

Given Data / Assumptions:

• The language in question is PHP with object oriented features enabled.
• We have classes that can define instance properties, instance methods, static properties, static methods, and class constants.
• Code examples may use variables such as $obj for objects and ClassName for classes.

Concept / Approach:
The arrow operator -> is used when you already have an object variable and you want to access a property or method that belongs to that concrete instance. In contrast, the scope resolution operator :: is used to access elements that belong to the class itself, such as static properties, static methods, and constants. It is also used with self, parent, and static keywords to refer to members in the current or parent class inside a class definition. In other words, -> works with object instances and :: works with class level access.

Step-by-Step Solution:
Step 1: Consider an instance method call. If you wrote $user = new User(); then you would call an instance method as $user->login(). This uses -> because login works on that particular object.Step 2: Consider a static method. If User defines a static method findById, you would normally call it as User::findById(10). This uses :: because you are working at the class level.Step 3: For a class constant defined as const ROLE_ADMIN = 1, you would access it as User::ROLE_ADMIN, again using :: and not ->.Step 4: Inside the class, you may see self::someStaticMethod() or parent::someMethod(), which again use :: to refer to static or parent members.Step 5: From these examples it is clear that -> is associated with object variables, while :: is associated with class names and static or constant members, which matches option A.

Verification / Alternative check:
If you try to access a static method with -> in strict coding styles, you will often receive warnings or notices that this usage is deprecated or incorrect. Similarly, trying to use :: on a normal instance property that is not static will give an error. This behaviour confirms that PHP enforces a difference between instance context and class context and that the description in option A is accurate.

Why Other Options Are Wrong:
Option B reverses the roles of the operators, which does not match PHP syntax or runtime behaviour. Option C claims that both operators are interchangeable, which is false and would result in errors in real code. Option D incorrectly restricts where each operator can be used and ignores the instance versus class distinction that actually matters.

Common Pitfalls:
A common mistake is to call static methods with -> out of habit, or to forget to declare a method as static when planning to call it with ::. Another pitfall is trying to access a normal instance property with ::, which will fail. Developers should remember a simple rule of thumb: if you have an object variable, use ->, and if you are referring to something that conceptually belongs to the class itself, use ::.

Final Answer:
-> is used to access instance methods and properties through an object variable, while :: is used to access static methods, static properties, and class constants through a class name or keywords like self and parent.