Java Generics Online Test – 3

1. What will be the output of the following Java program?

    import java.util.*;
    class Output
    {
        public static double sumOfList(List<? extends Number> list) 
        {
            double s = 0.0;
            for (Number n : list)
                s += n.doubleValue();
            return s;
        }
        public static void main(String args[])
        {
           List<Double> ld = Arrays.asList(1.2, 2.3, 3.5);
           System.out.println(sumOfList(ld));
        }
    }

2. Which of these types cannot be used to initiate a generic type?

3. What will be the output of the following Java program?

    public class BoxDemo
    {
        public static <U> void addBox(U u, 
           java.util.List<Box<U>> boxes)
          {
            Box<U> box = new Box<>();
            box.set(u);
            boxes.add(box);
          }
        public static <U> void outputBoxes(java.util.List<Box<U>> boxes)
        {
            int counter = 0;
            for (Box<U> box: boxes)
            {
                U boxContents = box.get();
                System.out.println("Box #" + counter + " contains [" + boxContents.toString() + "]");
                counter++;
            }
        }
        public static void main(String[] args)
        {
            java.util.ArrayList<Box<Integer>> listOfIntegerBoxes = new java.util.ArrayList<>();
            BoxDemo.<Integer>addBox(Integer.valueOf(10), listOfIntegerBoxes);
            BoxDemo.outputBoxes(listOfIntegerBoxes);
        }
    }

4. What will be the output of the following Java program?

    import java.util.*;
    public class genericstack <E>
    {
        Stack <E> stk = new Stack <E>();
	public void push(E obj) 
        {
            stk.push(obj);
	}
	public E pop() 
        {
            E obj = stk.pop();
	    return obj;
	}
    }
    class Output
    {
        public static void main(String args[])
        {
            genericstack <String> gs = new genericstack<String>();
            gs.push("Hello");
            System.out.print(gs.pop() + " ");
            genericstack <Integer> gs = new genericstack<Integer>();
            gs.push(36);
            System.out.println(gs.pop());
        }
    }

5. What will be the output of the following Java program?

    import java.util.*;
    public class genericstack <E>
    {
        Stack <E> stk = new Stack <E>();
	public void push(E obj)
        {
            stk.push(obj);
	}
	public E pop()
        {
            E obj = stk.pop();
	    return obj;
	}
    }
    class Output
    {
        public static void main(String args[]) 
        {
            genericstack <Integer> gs = new genericstack<Integer>();
            gs.push(36);
            System.out.println(gs.pop());
        }
    }

6. Which of these data type cannot be type parameterized?

7. What will be the output of the following Java program?

    import java.util.*;
    class Output
    {
        public static void addNumbers(List<? super Integer> list)
        {
            for (int i = 1; i <= 10; i++)
            {
                list.add(i);
            }
        }
        public static void main(String args[])
        {
           List<Double> ld = Arrays.asList();
           addnumbers(10.4);
           System.out.println("getList(2)");
        }
    }

8. Which of these instance cannot be created?