How does the Decorator pattern differ from inheritance?

How does the Decorator pattern differ from inheritance?

• A. Decorator replaces the component with a subclass.
• B. Decorator changes the interface to a new one.
• C. Decorator ensures a single instance.
• D. Decorator adds responsibilities by wrapping objects at runtime; inheritance adds behavior at compile time; decorators can stack.

Answer: (D)

The key idea is extending behavior by wrapping objects at runtime rather than through static inheritance. A decorator holds a reference to a component and implements the same interface, so it can add its own behavior before or after delegating to the wrapped component. This setup allows you to stack multiple decorators, combining features in flexible ways without changing existing classes. Inheritance, by contrast, adds behavior at compile time through subclassing, which fixes which features are present and often requires creating many subclasses to cover all combinations. Decorators preserve the original interface, so clients treat decorated and undecorated objects uniformly, and they enable dynamic composition of features.

The key idea is extending behavior by wrapping objects at runtime rather than through static inheritance. A decorator holds a reference to a component and implements the same interface, so it can add its own behavior before or after delegating to the wrapped component. This setup allows you to stack multiple decorators, combining features in flexible ways without changing existing classes. Inheritance, by contrast, adds behavior at compile time through subclassing, which fixes which features are present and often requires creating many subclasses to cover all combinations. Decorators preserve the original interface, so clients treat decorated and undecorated objects uniformly, and they enable dynamic composition of features.