An interface defines a contract (what methods exist) and supports multiple inheritance of type. An abstract class can share state and implementation, but you can extend only one class. Use interface for capability, abstract class for shared base behavior.
Advanced answer
Deep dive
Expanding on the short answer — what usually matters in practice:
Context (tags): interface, abstract-class, oop
JVM: memory (heap/stack), GC, and what drives latency.
Contracts: equals/hashCode/toString, mutability and consequences.
Explain the "why", not just the "what" (intuition + consequences).
Trade-offs: what you gain/lose (time, memory, complexity, risk).
Edge cases: empty inputs, large inputs, invalid inputs, concurrency.
Examples
A tiny example (an explanation template):
// Example: discuss trade-offs for "interface-vs-abstract-class-—-what’s-the-differe"
function explain() {
// Start from the core idea:
// An interface defines a contract (what methods exist) and supports multiple inheritance of
}
Common pitfalls
Too generic: no concrete trade-offs or examples.
Mixing average-case and worst-case (e.g., complexity).