Modern Java Features interview questions

Records, sealed types, pattern matching, and the language changes that reshape idiomatic code.

3 questions in Java & Spring.

Java and the Spring ecosystemA 22-minute read on how the topic fits together, before the questions.Java fundamentals75 short answers on one page, for revising rather than studying.

medium2

mediumConceptScenario

A teammate turns a JPA entity into a Java record because records are immutable. Where is that claim false, and where is a record the wrong type?

Java records have shallow immutability: fields are final, but a List or array component can still change through its reference unless the compact constructor copies it. A record cannot be a JPA entity, because the class and fields are final, it lacks a no-arg constructor, and providers subclass and populate entities.

5 minmid, senior

mediumConceptDesign

How do records, sealed types and pattern matching change the way you model a domain?

Together they let you write closed data hierarchies the compiler can check. A record declares that a type is its components, a sealed interface enumerates the permitted variants, and an exhaustive switch over record patterns turns adding a variant into a compile error at every place that handles them.

5 minmid, senior, staff

hard1

hardConceptScenario

You move a service from Java 11 to Java 21 and it fails at startup with InaccessibleObjectException. What changed, and what do you do about it?

Strong encapsulation of JDK internals became the default in JDK 16 and JDK 17 removed the option to relax it wholesale, so deep reflection into a package nobody opened now throws instead of warning. The fix is a targeted --add-opens for one module and package, or a library version that no longer needs one.

5 minmid, senior, staff, lead