Java OCA OCP Practice Question 3019

Question

Consider the following program: 

import java.util.*;

class ListFromVarargs {
    public static <T> List<T> asList1(T... elements) {
        ArrayList<T> temp = new ArrayList<>();
        for(T element : elements) {
             temp.add(element);/*from   w w w . j av a  2 s .  c  om*/
        }
        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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