Java OCA OCP Practice Question 1653

Question

Which functional interface, when entered into the blank below, allows the class to compile? 

package mypkg;//from www  .j  a va 2s. com
import java.util.*;
import java.util.function.*;


public class Main {
   private static void m(List<Double> prices,
                          scanner) {
      prices.forEach(scanner);
   }
   public static void main(String[] right) {
      List<Double> prices = Arrays.asList(1.2, 6.5, 3.0);
      m(prices,
            p -> {
               String result = p<5 ? "Correct" : "Too high";
               System.out.println(result);
            });
   }


}
  • A. Consumer
  • B. DoubleConsumer
  • C. Supplier<Double>
  • D. None of the above


D.

Note

The forEach() method requires a Consumer instance.

Option C can be immediately discarded because Supplier<Double> does not inherit Consumer.

Option B is also incorrect.

DoubleConsumer does not inherit from Consumer.

In this manner, primitive functional interfaces cannot be used in the forEach() method.

Option A seems correct, since forEach() does take a Consumer instance, but it is missing a generic argument.

Without the generic argument, the lambda expression does not compile because the expression p<5 cannot be applied to an Object.

The correct functional interface is Consumer<Double>, and since that is not available, Option D is the correct answer.




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