| 1 | What is the Strategy pattern, and how do Java 8's functional interfaces and lambdas make implementing it significantly more concise than the traditional interface-plus-implementation-classes approach? Java › Design Patterns in Java | Java | Design Patterns in Java | Intermediate |
| 2 | What is the Java Collections Framework, and what are the core interfaces (List, Set, Map, Queue) at its foundation? Java › Collections Framework | Java | Collections Framework | Beginner |
| 3 | What is the difference between the Iterable and Iterator interfaces, and how does the enhanced for-each loop rely on them? Java › Collections Framework | Java | Collections Framework | Beginner |
| 4 | How do you retrieve all constants of an enum type, and how would you iterate over them? Java › Enums | Java | Enums | Beginner |
| 5 | What is a functional interface, and what are the four core functional interfaces in java.util.function (Function, Predicate, Consumer, Supplier)? Java › Functional Interfaces & Method References | Java | Functional Interfaces & Method References | Beginner |
| 6 | What are the four kinds of method references in Java (static, instance-bound, instance-unbound, and constructor), and how does the compiler determine which form applies? Java › Functional Interfaces & Method References | Java | Functional Interfaces & Method References | Intermediate |
| 7 | How do the default methods andThen() and compose() on Function work, and what's the difference between them for chaining transformations? Java › Functional Interfaces & Method References | Java | Functional Interfaces & Method References | Intermediate |
| 8 | What is the difference between UnaryOperator<T> and Function<T,T>, and why does UnaryOperator exist as a separate, more specific interface? Java › Functional Interfaces & Method References | Java | Functional Interfaces & Method References | Intermediate |
| 9 | How do the primitive-specialized functional interfaces (IntFunction, ToIntFunction, IntPredicate, IntUnaryOperator, etc.) avoid the performance cost of autoboxing, and when should you prefer them over the generic equivalents? Java › Functional Interfaces & Method References | Java | Functional Interfaces & Method References | Intermediate |
| 10 | How does the Predicate interface's default methods and(), or(), and negate() enable composing complex boolean conditions from simpler ones? Java › Functional Interfaces & Method References | Java | Functional Interfaces & Method References | Intermediate |
| 11 | What is the difference between a Consumer<T> and a BiConsumer<T,U>, and how would you use BiConsumer for operations needing two inputs but no return value, such as Map.forEach()? Java › Functional Interfaces & Method References | Java | Functional Interfaces & Method References | Intermediate |
| 12 | How do you write a generic method (as opposed to a generic class), and how does the compiler infer the type parameter from the arguments passed at a call site? Java › Generics | Java | Generics | Intermediate |
| 13 | What is LINQ, and how does it simplify querying collections compared to writing manual loops? C# › LINQ | C# | LINQ | Intermediate |
| 14 | How would you implement a custom Comparator with multiple sort criteria (e.g., sort by last name, then by first name as a tiebreaker) using the Comparator.comparing() and thenComparing() fluent API? Java › Collections Framework | Java | Collections Framework | Advanced |
| 15 | How would you implement a custom compareTo()-based ordering for an enum that differs from its natural declaration-order ordering, given Comparable's default implementation uses ordinal()? Java › Enums | Java | Enums | Advanced |
| 16 | How would you use BiFunction combined with Stream's reduce() to implement a custom aggregation, and how does this relate to the more general concept of a fold operation in functional programming? Java › Functional Interfaces & Method References | Java | Functional Interfaces & Method References | Advanced |
| 17 | How would you use a local class defined within a method to implement a fairly complex, stateful callback that needs multiple methods and constructor parameters, where a lambda expression genuinely wouldn't suffice? Java › Inner Classes & Anonymous Classes | Java | Inner Classes & Anonymous Classes | Advanced |