Java Interface Test – 3

1. 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("[" + boxContents.toString() + "]");
                counter++;
            }
        }
        public static void main(String[] args)
        {
            java.util.ArrayList<Box<Integer>> listOfIntegerBoxes = new java.util.ArrayList<>();
            BoxDemo.<Integer>addBox(Integer.valueOf(0), listOfIntegerBoxes);
            BoxDemo.outputBoxes(listOfIntegerBoxes);
        }
    }

2. Which of these is an correct way of defining generic class?

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. Which of the following is an incorrect statement regarding the use of generics and parameterized types in Java?

6. Why are generics used?

7. Which of these type parameters is used for a generic class to return and accept a number?

8. Which of these type parameters is used for a generic class to return and accept any type of object?

9. 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);
        }
    }

10. Which of the following reference types cannot be generic?