Aporeon

Technical interview practice, from one developer to another.

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Comparison questionMedium~7 min

When would you use HashMap, LinkedHashMap, or TreeMap?

Chooses among common Java map implementations by lookup behavior, iteration order, sorting, range operations, and key contracts.

Java

Practice drill

Comparison questionMedium~7 min

When would you use Spring application events instead of durable messaging?

Separates in-process decoupling from durable cross-process delivery and makes timing, failure, and transaction expectations explicit.

JavaSpring Boot

Practice drill

Architecture scenarioHard~10 min

When would you write a custom HealthIndicator for a Spring Boot service?

Adds dependency health only when it supports a specific operational decision and can be checked cheaply and safely.

JavaSpring Boot

Practice drill

Architecture scenarioHard~10 min

Where should a Java service catch, translate, or rethrow exceptions?

Places exception handling at boundaries that can recover, add meaningful context, or translate abstraction levels while preserving the cause.

Java

Practice drill

Architecture scenarioHard~10 min

Where should transaction boundaries be placed in a Spring application?

Places a short transaction around one application use case while keeping remote calls, user interaction, and bulk work outside.

JavaSpring Boot

Practice drill

Comparison questionMedium~7 min

Why are Java arrays covariant while generics are invariant?

Contrasts runtime-checked array covariance with compile-time-safe generic invariance and explains why generic arrays are restricted.

Java

Practice drill

Concept questionMedium~7 min

Why are raw types and unchecked warnings risky in Java?

Treats raw types as a legacy compatibility boundary that can introduce heap pollution and delayed runtime failures.

Java

Practice drill

Concept questionMedium~7 min

Why are side effects risky in Java stream operations?

Explains interference, stateful lambdas, execution-order assumptions, safe collection, and visibility of unavoidable effects.

Java

Practice drill

Debugging scenarioMedium~7 min

Why does ConcurrentModificationException happen, and how do you modify a collection safely?

Explains fail-fast iteration, safe removal patterns, structural modification, and why the exception is not a concurrency guarantee.

Java

Practice drill

Concept questionEasy~5 min

Why does Java use generics?

Explains generics as compile-time type-safe reuse that improves API contracts and removes scattered casts.

Java

Practice drill

Comparison questionMedium~7 min

Why is composition often preferred over inheritance in Java?

Explains how delegation preserves replaceable behavior and narrower coupling while recognizing valid inheritance cases.

Java

Practice drill

Concept questionMedium~7 min

Why is List<Integer> not a subtype of List<Number> in Java?

Explains Java generic invariance through the unsafe write that subtype assignment would otherwise permit.

Java

Practice drill

Concept questionMedium~7 min

Why is String immutable, and what does string pooling change?

Separates String immutability from interning and connects both to safe sharing, equality, concatenation, and practical performance.

Java

Practice drill

Concept questionMedium~7 min

Why must equals and hashCode agree in Java?

Connects Java's equality and hash contracts to real HashMap and HashSet behavior, including mutable-key failures.

Java

Practice drill

Concept questionMedium~7 min

Why must local variables captured by a Java lambda be effectively final?

Explains Java lambda capture through copied local values, mutable referenced objects, lifetime, and safe state handling.

Java

Practice drill

Architecture scenarioMedium~7 min

Why use request and response DTOs in a Spring API?

Keeps JSON binding, validation, writable fields, and response evolution separate from domain and persistence models.

JavaSpring Boot

Practice drill

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