Top 4 Polymorphism Interview Questions

Browse 4 real-world technical and behavioral interview questions about Polymorphism. Review scenarios, edge cases, and architectural best practices.

Give me a subclass that the compiler accepts but that still breaks the Liskov substitution principle. What rule does it break?

Substitutability is a claim about behaviour, and signatures carry none of it. A subclass that rejects an argument its supertype accepted has strengthened a precondition, which the compiler cannot see: the code type-checks, and it breaks callers that were written correctly against the base type.

mediumconcept

Where does encapsulation or polymorphism change a design, and how do you decide between composition and inheritance?

Encapsulation earns its place when a class owns an invariant that callers would otherwise each have to enforce, and polymorphism when a conditional grows with every new requirement. Composition versus inheritance is decided on evidence: how many axes vary, and whether every inherited operation is honest.

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What are the four pillars of OOP, and what is the difference between abstraction and encapsulation?

Encapsulation, inheritance, polymorphism and abstraction are worth stating as consequences rather than definitions - what each one buys you and what it costs. Abstraction decides what a type means to its caller; encapsulation protects how that meaning is upheld.

easyconcept

When you call an overridden method through a base-class reference, how does the runtime know which implementation to run?

The compiler cannot know, so it emits an indirect call through a per-class table of function pointers that the object carries a reference to. The lookup itself is a couple of memory accesses; the real cost is the optimisations the compiler cannot perform when the target is not known until run time.

mediumconcept