Java SE 8 Programmer II Exam: Birdie Class Compilation

Java SE 8 Programmer II Exam

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Question

Given: class Bird{ public void fly (){System.out.print("Can fly"); } } class Penguin extends Bird{ public void fly (){System.out.print("Cannot fly"); } } and the code fragment: class Birdie { public static void main (String [ ] args){ fly( ( ) -> new Bird ( )); fly (Penguin : : new); } /* line n1 */ } Which code fragment, when inserted at line n1, enables the Birdie class to compile?

Answers

A. static void fly (Consumer bird) { bird :: fly (); }

B. static void fly (Consumer bird) { bird.accept( ) fly (); }

C. static void fly (Supplier bird) { bird.get( ) fly (); }

D. static void fly (Supplier bird) { bird::fly(); }

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Explanations

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A. B. C. D.

The code snippet defines two classes: Bird and Penguin, where Penguin is a subclass of Bird. Both classes have a method fly() that prints a message indicating whether the bird can fly or not.

The Birdie class has a main method, which calls the fly method twice, each time with a different argument.

The problem with the given code is that there is no fly method defined in the Birdie class or in any of its superclasses or imported classes. Therefore, the code will not compile unless a valid fly method is added.

Option A:

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static void fly(Consumer<Bird> bird) {     bird::fly(); }

This option defines a static fly method that takes a Consumer<Bird> argument. A Consumer is a functional interface that takes an argument and returns nothing. In this case, the Consumer takes a Bird argument and calls its fly method. This option is valid because both Bird and Penguin are Bird instances, so they can be passed as arguments to the fly method.

Option B:

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static void fly(Consumer<? extends Bird> bird) {     bird.accept().fly(); }

This option defines a static fly method that takes a Consumer<? extends Bird> argument. This means that the Consumer can take any object that extends Bird. In the method body, the accept method of the Consumer is called, which returns a Bird object, and then the fly method of the returned object is called. This option is valid because both Bird and Penguin are Bird instances, so they can be passed as arguments to the fly method.

Option C:

scss
static void fly(Supplier<Bird> bird) {     bird.get().fly(); }

This option defines a static fly method that takes a Supplier<Bird> argument. A Supplier is a functional interface that takes no arguments and returns an object of the specified type. In this case, the Supplier returns a Bird object, and then the fly method of the returned object is called. This option is valid because both Bird and Penguin are Bird instances, so they can be returned by the Supplier.

Option D:

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static void fly(Supplier<? extends Bird> bird) {     bird.get().fly(); }

This option is similar to option C, but the Supplier can take any object that extends Bird. This option is also valid because both Bird and Penguin are Bird instances, so they can be returned by the Supplier.

Therefore, options A, B, C, and D are all valid solutions that would allow the Birdie class to compile. The correct option will depend on the specific requirements of the program.

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