What limitations exist when defining subclasses in object-oriented programming?

The following restrictions exist when defining subclasses in object-oriented programming:

• Inheritance from final classes: In languages that support the final modifier (e.g., Java), inheritance from classes declared as final is not allowed.
• Inheritance from specific classes: A subclass can only inherit from one class (single inheritance) if the language does not support multiple inheritance (e.g., Java). In C++, multiple inheritance is allowed but can lead to complexity.
• Access to superclass members: A subclass cannot directly access private members of the superclass, only through superclass methods.
• Constructors: Superclass constructors are not inherited; they must be explicitly called from the subclass constructor.
• Restrictions on overriding: Some methods may be declared as final or sealed, which prohibits their overriding in subclasses.

These restrictions help control the class hierarchy and ensure the safety and predictability of the program's behavior.