25-Comp-B11 Advanced Software Design · December 2014
Question 7 of 26: Polymorphism, Dynamic Binding, Overloading, Overriding
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
98-Comp-B11 Advanced Software Design — National Exams, December 2014. 3 hours, closed book, no calculator permitted. The paper is organized into five parts, and candidates were instructed to answer any three (3) questions in Part I, any four (4) in Part II, any four (4) in Part III, any two (2) in Part IV, and any two (2) in Part V — only the first questions answered, in each part, as they appear in the answer book are marked. All questions carry equal weight, so the 15 questions actually marked (3+4+4+2+2 of 26) each count for 100/15 ≈ 6.7% of the paper. All 26 questions are answered below for completeness.
Reference texts: Sommerville, Software Engineering (10th ed., Pearson) — software processes, requirements engineering, agile methods, design principles; Pressman, Software Engineering: A Practitioner's Approach (9th ed.) — supplementary process and quality coverage; Gamma, Helm, Johnson & Vlissides (GoF), Design Patterns: Elements of Reusable Object-Oriented Software — structural/behavioural pattern catalogue (Proxy, Bridge, Strategy, Observer, Template Method, Composite, etc.); Sebesta, Concepts of Programming Languages (12th ed.) — polymorphism, dynamic binding, inheritance and language-level object semantics (also underpins the Java/C++ discussion in Part V); Brown, Malveau, McCormick & Mowbray, AntiPatterns: Refactoring Software, Architectures, and Projects in Crisis — anti-pattern catalogue (Question 18). Bertrand Meyer's Object-Oriented Software Construction is cited by name where the paper's own vocabulary (design by contract, open–closed principle) originates there; Barbara Liskov's 1987 substitutability paper is likewise cited by name for Question 11.
(a) Polymorphism is the ability of a single name (a method call, a variable) to refer to, or be applied to, objects of more than one type, so that code written against a general interface can operate uniformly over different concrete types without knowing which one it holds.
(b) Dynamic binding (late binding) is the RUNTIME mechanism that resolves a call to a polymorphic operation to the actual implementing method based on the object's real, runtime type — not its declared, compile-time type — typically implemented via a per-class dispatch table (vtable) that is consulted at the moment of the call.
(c) Overloading is defining multiple methods that share the same name but differ in parameter signature (number/type of parameters). It is resolved entirely at COMPILE time, by the compiler matching the call site's argument types against the available signatures — no runtime dispatch is involved.
(d) Overriding is a subclass supplying its own implementation of a method already declared in a superclass, with an IDENTICAL signature. This is precisely what dynamic binding dispatches between at runtime: when client code calls the method through a base-type reference, dynamic binding selects whichever override matches the object's actual runtime type.
How they relate. Polymorphism is the general concept (one interface, many forms); overriding plus dynamic binding together are the runtime MECHANISM implementing one specific and very common kind of polymorphism (inclusion/subtype polymorphism, exercised through inheritance). Overloading is a DIFFERENT kind of polymorphism entirely (ad hoc polymorphism) that is resolved statically at compile time and never touches the vtable/dynamic-dispatch mechanism at all. A common confusion is treating overloading and overriding as the same idea because both "give a method multiple forms" — they do not share a resolution mechanism, and confusing them is exactly the bug analyzed in Question 25.
