Reuse mechanisms in C#.NET: which of the following provide code reuse in typical C# design? 1) Inheritance 2) Encapsulation 3) Templates 4) Containership (composition/aggregation) 5) Polymorphism

Introduction / Context:
Code reuse is a principal OO goal. In C#, the most common reuse mechanisms are inheritance (specialization and reuse of base behavior) and containership/composition (reusing existing types as parts of larger types).

Given Data / Assumptions:

• “Templates” here maps to C++ terminology; in C#, the equivalent is generics, which facilitate type reuse but are not a direct code-reuse mechanism like inheritance/composition.
• Polymorphism enables substitutability but is built on inheritance/interfaces rather than being a reuse mechanism by itself.
• Encapsulation is about information hiding, not reuse per se.

Concept / Approach:
Inheritance allows derived classes to reuse and extend base behavior. Containership (composition/aggregation) lets a class reuse existing classes by holding them as fields and delegating work. While generics and polymorphism are powerful, the classic “reuse mechanisms” are inheritance and composition.

Step-by-Step Solution:

Verification / Alternative check:
Review design patterns: composition-over-inheritance is a maxim precisely because both are established reuse techniques.

Why Other Options Are Wrong:
They emphasize concepts that are important but either do not directly provide code reuse (encapsulation) or are language features/behaviors rather than reuse mechanisms (generics/polymorphism).

Common Pitfalls:
Equating “polymorphism” with reuse; conflating C++ templates with C# generics and their role.

Final Answer:
1, 4