Microsoft Certified Solutions Developer (MCSD) Certification Practice Test

What best describes the difference between implementing an interface and inheriting from a class?

1. Interfaces allow multiple inheritance; classes do not

2. Both represent an "is-a" relationship

3. Implementing an interface restricts access to members

4. Classes cannot implement interfaces

The correct answer is: Interfaces allow multiple inheritance; classes do not

The choice highlighting that interfaces allow multiple inheritance while classes do not is accurate. In programming languages like C# or Java, a class can inherit from only one base class, enforcing a single inheritance model. However, a class can implement multiple interfaces, thereby allowing it to inherit behavior from multiple sources. This characteristic is particularly useful for achieving polymorphism, allowing a class to exhibit behaviors defined in various interfaces. Using interfaces also enables flexibility as they define a contract that multiple classes can implement in their own way, promoting a more modular design. This functionality is not available when using class inheritance, which can lead to a rigid and less adaptable structure. The other options present misconceptions about object-oriented principles. For instance, not all relationships represented by interfaces and classes fit neatly into "is-a" relationships; interfaces are often "can-do" capabilities rather than strict hierarchical classifications. Additionally, implementing an interface does not restrict access to members; rather, it defines specific methods that must be implemented, while classes typically manage access through their visibility modifiers. Lastly, classes are fully capable of implementing interfaces, often utilizing this feature to integrate various functionalities.