การสืบทอดและการเขียนทับเมธอด

Inheritance lets a class reuse and extend another class. The new subclass gets all the methods and properties of its superclass, then adds or changes behavior.

The colon syntax in the interface declares the superclass. Here Dog inherits from Animal.

A subclass automatically has the superclass's public methods and properties — no need to redeclare them.

To change inherited behavior, redeclare a method with the same name in the subclass. This is overriding.

Use super to invoke the superclass version, extending rather than replacing its behavior.

Custom initializers almost always call [super init] first to set up inherited state, then add their own.

A superclass-typed variable can hold any subclass instance. The correct overridden method runs at runtime — this is polymorphism.

Initializers return instancetype, which adapts to the actual class being created — safer than hardcoding the type.

Objective-C is dynamic. You can ask an object about its class.

Almost every class ultimately inherits from NSObject, which provides core behavior like alloc, init, isEqual:, and memory management hooks.

Favor shallow hierarchies. Use inheritance for genuine is-a relationships; for shared behavior across unrelated classes, prefer protocols and categories instead.

Test your inheritance knowledge.

You learned inheritance in Objective-C:

• Subclass with the : Superclass syntax
• Inherited methods and properties come for free
• Override methods to change behavior
• Use super to extend the parent version
• Polymorphism picks the right method at runtime

Inheritance and polymorphism are pillars of OOP in Objective-C.