Java MCQ's on Constructors

This test contains 10 questions based on Constructors.
Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers.

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You Get +1 for each correct answer and -0.25 for each incorrect answer

Time Left - minutes : seconds

What is the return type of Constructors?

int	float
void	None of these

D

Constructors does not have any return type, not even void.

Which keyword is used by method to refer to the object that invoked it?

import	catch
this	super

C

this keyword is used by the method to refer to the object that invoked it. this keyword can also be used to refer to any member that is within the class e.g instance variables , functions or even objects.  

Which of the following is a method having same name as that of its class?

finalize	constructor
delete	class

B

A constructor is a method that initializes an object immediately upon creation. It has the same name as that of class in which it resides. A constructor does not have any return type and is mostly used to initialize the members of a class when an object of a class is made. 

Which operator is used by Java run time implementations to free the memory of an object when it is no longer needed?

delete	free
new	None of these

D

 Java handles deallocation of memory automatically, we do not need to explicitly delete an element. Garbage collection only occurs during execution of the program. When no references to the object exist, that object is assumed to be no longer needed, and the memory occupied by the object can be reclaimed.

Which function is used to perform some action when the object is to be destroyed?

finalize()	delete()
main()	None of these

A

finalize() is the method that is called by the to perform some action or task before the object is made ready for garbage collection.

What is the output of this program?

class Box {
        int width;
        int height;
        int length;
        int volume;
        public Box() {
            width = 5;
            height = 5;
            length = 6;
        }
        void volume() {
             volume = width*height*length;
        } 
    }    
    class Output {
        public static void main(String args[])
        {
            Box obj = new Box();
            obj.volume();
            System.out.println(obj.volume);
        }
   }

100	150
200	250

B

new Box() will make an object of class Box and assign values to the instance variables. obj.volume() will calculate the volume and assign value "5 * 5 * 6" to variable "volume". obj.volume will print the value assigned to the variable volume what will be 150.

What will be the output of the following program ?

class Equality {
        Integer x;
        Integer y;
        boolean isequal() {
            return(x == y);  
        } 
    }    
    class Output {
        public static void main(String args[])
        {
            Equality obj = new Equality();
            obj.x = 5;
            obj.y = 5;
            System.out.println(obj.isequal());        } 
    }

True	False
0	1

A

Since both the variables are "x" and "y" are equal assigned with value 5, it will give the output "true"

What will be the output of the following program ?

class Box {
        int width;
        int height;
        int length;
        int volume;
        void finalize() {
            volume = width*height*length;
            System.out.println(volume);
        }
        protected void volume() {
            volume = width*height*length;
            System.out.println(volume);
       } 
    }    
    class Output { 
        public static void main(String args[])
        {
            Box obj = new Box();
            obj.volume();
        } 
    }

Compilation error	Runtime error
0	100

C

The program will compile successfully. When we create the object of a class all the instance variables that are not initialized are initialized with a default value 0. Thus it will give an output "0"

Which of the folowing stements are incorrect?

Default constructor is called at the time of declaration of the object if a constructor has not been defined.	finalize() method is called when a object goes out of scope and is no longer needed.
finalize() method must be declared protected.	Constructor can be parameterized.

B

finalize() method is called just prior to garbage collection. it is not called when object goes out of scope.

What will be the output of this program?

class Area {
        int width;
        int length;
        int area;
        public Area(int width, int length) {
            this.width = width;
            this.length = length;
        }
 
    }    
    class Output {
        public static void main(String args[])
        {
            Area obj = new Area(5 , 6);
            System.out.println(obj.length + " " + obj.width);        
        } 
    }

0 0	5 5
5 6	6 5

D

new Area(5,6) will set width = 6 and height = 5, thus the output will be "6 5"

Finish Test