Java OCA OCP Practice Question 1621

Question

Which fills in the blank in the method signature to allow this code to compile? 

import java.util.*;
public class Main {
   private static <___, U> U add(T list, U element) {
      list.add(element);//w ww.  j av  a2s  . c om
      return element;
   }
   public static void main(String[] args) {
      List<String> values = new ArrayList<>();
      add(values, "A");
      add(values, "A");
      add(values, "B");
      System.out.println(values);
   }
}
  • A. ? extends Collection<U>
  • B. ? implements Collection<U>
  • C. T extends Collection<U>
  • D. T implements Collection<U>


C.

Note

The ? is an unbounded wildcard.

It is used in variable references but is not allowed in declarations.

In a static method, the type parameter specified inside the <> is used in the rest of the variable declaration.

Since it needs an actual name, Options A and B are incorrect.

We need to specify a type constraint so we can call the add() method.

Regardless of whether the type is a class or interface, Java uses the extends keyword for generics.

Option D is incorrect, and Option C is the answer.




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