Quiz: Functional Interfaces in Java 8 Explained

1. What is a functional interface in Java 8?

AAn interface with no methods at allBAn interface that has exactly one abstract methodCAn interface whose methods are all default methodsDAn interface that extends java.util.function.Function

2. What is the primary purpose of functional interfaces?

ATo let implementations of their abstract method be passed around as lambda expressions, enabling behaviour parameterizationBTo replace abstract classes completelyCTo make code run on multiple threads automaticallyDTo allow multiple inheritance of state

3. Which annotation can mark an interface explicitly as a functional interface?

A@FunctionalB@LambdaC@SingleMethodD@FunctionalInterface

4. What does the compiler do when an interface annotated with @FunctionalInterface has two abstract methods?

AIt ignores the annotationBIt reports a compile-time errorCIt turns the second method into a default methodDIt generates a warning only at runtime

5. Is the @FunctionalInterface annotation mandatory for an interface to be a functional interface?

AYes, without it a lambda cannot implement the interfaceBYes, but only for interfaces in java.util.functionCNo, it is informative - any interface with a single abstract method qualifiesDNo, because functional interfaces must be declared with the functional keyword

6. Which of these interfaces, which existed before Java 8, is a functional interface?

Ajava.lang.RunnableBjava.util.ListCjava.io.SerializableDjava.lang.Cloneable

7. What is the single abstract method of java.util.concurrent.Callable<V>?

Avoid run()BV get()CV apply(V v)DV call() throws Exception

8. Which abstract method does java.util.function.Predicate<T> declare?

AT get()Bboolean test(T t)Cvoid accept(T t)DR apply(T t)

9. The tutorial groups functional interfaces into three types. Which of these is NOT one of them?

ACustom (user-defined) functional interfacesBFunctional interfaces that existed before Java 8, such as RunnableCNew pre-defined functional interfaces in java.util.functionDMarker interfaces with no methods, such as Serializable

10. A user-defined interface has one abstract method and no @FunctionalInterface annotation. Can a lambda expression implement it?

ANo, the annotation is required for lambdasBOnly if the interface is in the java.util.function packageCYes, because it has a single abstract methodDOnly if the method returns void