What mechanism allows methods to be called on an object without knowing its type at compile time?

Polymorphism is the mechanism that allows methods to be called on an object without needing to know its specific type at compile time. This capability is essential in object-oriented programming, as it promotes flexibility and reusability of code.

When a method is called on an object, the specific method that gets executed is determined at runtime based on the actual object type. This behavior allows developers to write more generic and reusable code. For instance, if a method is defined in a base class and overridden in a derived class, polymorphism enables the base class reference to invoke the overridden method of the derived class during execution. This approach not only supports dynamic method binding but also integrates well with interfaces and abstract classes, further enhancing code organization and structure.

In contrast, other concepts such as encapsulation, inheritance, and abstraction do not directly provide this capability. Encapsulation is about restricting access to certain components of an object, inheritance deals with creating new classes based on existing ones, and abstraction focuses on exposing only the relevant properties and methods while hiding implementation details. None of these concepts allow for calling methods on an object without knowing its type at compile time, which is the defining feature of polymorphism.