Java OCA OCP Practice Question 3268

Question

Consider the following program: 

import java.util.ArrayList;
import java.util.List;

class ListFromVarargs {
   public static <T> List<T> asList1(T... elements) {
      ArrayList<T> temp = new ArrayList<>();
      for (T element : elements) {
         temp.add(element);/* w w  w  .  jav a2s. c  o m*/
      }
      return temp;
   }

   public static <T> List<?> asList2(T... elements) {
      ArrayList<?> temp = new ArrayList<>();
      for (T element : elements) {
         temp.add(element);
      }
      return temp;
   }

   public static <T> List<?> asList3(T... elements) {
      ArrayList<T> temp = new ArrayList<>();
      for (T element : elements) {
         temp.add(element);
      }
      return temp;
   }

   public static <T> List<?> asList4(T... elements) {
      List<T> temp = new ArrayList<T>();
      for (T element : elements) {
         temp.add(element);
      }
      return temp;
   }
}

Which of the asList() definitions in this program will result in a compiler error? 

a)The definition of asList1 will result in a compiler error.
b)The definition of asList2 will result in a compiler error.
c)The definition of asList3 will result in a compiler error.
d)The definition of asList4 will result in a compiler error.
e)None of the definitions (asList1, asList2, asList3, asList4) will result in a compiler error.



b)

Note

In the asList2 method definition, temp is declared as ArrayList<?>.

Since the template type is a wild-card, you cannot put any element (or modify the container).

Hence, the method call temp.add(element); will result in a compiler error.




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