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25-Comp-B11 Advanced Software Design · December 2019

Question 28 of 28: Modular Programming in C++ and Java

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

17-Comp-B11 Advanced Software Design — National Exams, December 2019. 3 hours, closed book exam with one aid sheet allowed (written on both sides), no calculator permitted. The paper is organized into five parts, and candidates were instructed to answer any five (5) questions in Part I, any three (3) in Part II, any four (4) in Part III, any two (2) in Part IV, and any five (5) 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 19 questions actually marked (5+3+4+2+5 of 28) each count for 100/19 ≈ 5.26% of the paper. All 28 questions are answered below for completeness.

Reference texts: Sommerville, Software Engineering (10th ed., Pearson) — software processes, requirements engineering, design principles, testing, dependability; 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 — creational/structural/behavioural pattern catalogue and the "program to an interface, not an implementation" / "favor object composition over class inheritance" principles; Sebesta, Concepts of Programming Languages (12th ed.) — polymorphism, dynamic binding, visibility, and multiple inheritance semantics; Bertrand Meyer, Object-Oriented Software Construction — design by contract, preconditions/postconditions/class invariants; Barbara Liskov's 1987 substitutability paper for Question 12; Karl Wiegers, Software Requirements (3rd ed.); Myers, The Art of Software Testing, for Question 6.

PART I — General Principles (answer any 5 of 7)

Question 28: Modular Programming in C++ and Java (Part V)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Modular programming decomposes a program into separately-compilable/loadable units, each with a well-defined public interface, hiding its internal implementation details, and communicating with other units only through that interface.

C++. Traditionally implemented as a header (.h, declarations = the public interface) paired with a source file (.cpp, the implementation), each unit compiled independently and linked together; namespaces group related declarations and avoid name collisions across units.

// Calculator.h  (the public interface)
class Calculator {
public:
    int add(int a, int b);
};
// Calculator.cpp  (the hidden implementation)
#include "Calculator.h"
int Calculator::add(int a, int b) { return a + b; }
// main.cpp -- depends only on the header, links against the compiled .cpp
#include "Calculator.h"

C++20 introduces a language-level module feature that replaces the header/source convention with a true compiled module interface (faster builds, no macro/preprocessor leakage across module boundaries), but the header/source pattern remains the more widely deployed approach.

Java. Modularity is built in more directly: packages group related classes under a namespace, and, since Java 9, the Java Platform Module System (JPMS) lets a module-info.java file declare which packages a module exports (its public API) and which other modules it requires. This gives STRONG encapsulation at the module level: a package that is not exported is invisible to every other module regardless of the individual visibility (Question 23) of the classes inside it — a guarantee ordinary package-private visibility alone could not make, since any class in the same package could still see it.

// module-info.java
module com.finance.core {
    exports com.finance.api;   // only this package is visible externally
    requires java.base;
}
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