In Java, which King class best represents the relationship "King has a best friend who is a Soldier"?

Introduction / Context:
Object-oriented design in Java distinguishes between inheritance (is a relationships) and association or composition (has a relationships). The sentence King has a best friend who is a Soldier describes an association, not that a King is a Soldier. Interviewers use questions like this to check whether you can correctly map a natural language description into an appropriate class design in Java.

Given Data / Assumptions:

• We have a King class that models a king as a domain object.
• We have a Soldier class that models soldiers as separate domain objects.
• The requirement states that the king has a best friend who is of type Soldier.
• We want to choose the correct Java class declaration that represents this relationship.

Concept / Approach:
The phrase King has a best friend who is a Soldier describes a has a association between King and Soldier. This means the King class should contain a reference to a Soldier object, typically as a field. It does not say that a king is a soldier, so inheritance (extends) is not appropriate. Nor does it say that King must behave like a Soldier interface; instead, it simply refers to a single associated Soldier instance. Therefore, the best representation is a King class with a private Soldier field named bestFriend, modeling a one to one association between a King instance and its best friend Soldier instance.

Step-by-Step Solution:
Step 1: Identify the relationship type: the phrase "has a best friend" describes ownership or association, not identity. Step 2: Recognize that in Java, has a relationships are typically implemented as fields referencing other objects. Step 3: Examine the candidate declarations and look for one where King contains a Soldier field rather than extending or implementing Soldier. Step 4: See that class King { private Soldier bestFriend; } declares an instance field of type Soldier inside King, matching the description. Step 5: Conclude that option with a private Soldier bestFriend field correctly models a King who has a best friend who is a Soldier.

Verification / Alternative check:
You can extend this design to code by adding constructors and methods. For example, King could have a constructor King(Soldier bestFriend) and a getter getBestFriend(), which makes the relationship explicit in the API. In UML diagrams, this would be drawn as an association from King to Soldier, not as an inheritance arrow. This aligns with best practices that reserve inheritance for is a relationships and use composition or association for has a relationships.

Why Other Options Are Wrong:
Option A, class King extends Soldier { }, implies that every King is a kind of Soldier, which does not match the requirement about having a best friend. Option B, class King implements Soldier { }, suggests that King must conform to Soldier behavior as an interface, again modeling is a rather than has a. Option C is syntactically incorrect and conceptually unclear because BestFriend is used as a type name and Soldier as a field name, which does not define a clear has a relationship.

Common Pitfalls:
A common pitfall is overusing inheritance and modeling every relationship with extends, which leads to fragile and overly complex hierarchies. Another mistake is poor naming that confuses types and fields, making code hard to understand. Developers should remember to use composition and association for has a relationships, reserving inheritance for genuine is a relationships, which keeps designs simpler and more flexible.

Final Answer:
The best representation is class King { private Soldier bestFriend; }, which models a King object that has a best friend who is a Soldier through a private Soldier field.