Which stream operation in Java 8 is used to flatten a stream of collections (e.g. Stream<List<String>>) into a single un-nested stream (Stream<String>)?
Option C is correct. flatMap() applies a 1-to-N mapping function to each element and flattens the resulting streams into a single composite output stream.
Which functional interface in java.util.function accepts two arguments of types T and U and produces a result of type R?
Option B is correct. BiFunction<T, U, R> represents a function that accepts two arguments (T, U) and produces a result (R) via its R apply(T t, U u) method.
Which functional interface in java.util.function takes a single argument of type T and returns a boolean value?
Option A is correct. Predicate<T> represents a boolean-valued function of one argument, evaluated using test(T t). Used extensively in stream filtering.
Which functional interface in java.util.function accepts no arguments and produces a result of type T?
Option B is correct. Supplier<T> represents a supplier of results with a single get() method taking no arguments.
Which functional interface in java.util.function accepts a single argument of type T and returns no result (void return)?
Option E is correct. Consumer<T> represents an operation that accepts a single input argument and returns no result via accept(T t).