Which interface in the java.util.function package can return a primitive type?

Question

Options

• AToDoubleFunction
• BFunction
• CBiFunction
• DLongConsumer

• A
  83% (20)
• B
  8% (2)
• C
  4% (1)
• D
  4% (1)

Explanation

ToDoubleFunction<T> is correct because its functional method applyAsDouble(T value) returns a primitive double, not a boxed Double object - this is precisely the design intent of the ToXxxFunction family in java.util.function.

Function<T,R> and BiFunction<T,U,R> both use generic return types (R), which must be object types - Java generics cannot represent primitives, so these always return a reference type, not a primitive.

LongConsumer does accept a primitive long, but it's a Consumer - its accept(long value) method returns void, meaning it produces no value at all.

Memory tip: Look for the To prefix paired with a primitive type name (ToDouble, ToInt, ToLong) - these are the interfaces that return primitives. Meanwhile, interfaces starting with the primitive name directly (like LongConsumer, IntSupplier) describe what they accept or supply, not necessarily what they return.

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