Inheritance and Polymorphism

Question 1

class reusability has two forms …. and ….

Answer 1

composition and inheritance

Question 2

composition is called a ….

Answer 2

has- a

Question 3

has - a or composition means

Answer 3

placing a reference / object of a class in another class

Question 4

inheritance is (is-a)

Answer 4

extending a class with another class

Question 5

inheritance means

Answer 5

that a new class inherits from an existing class, it inherits all its members and characteristics

Question 6

subclass constructor has to call… directly or indirectly

Answer 6

base/parent class

Question 7

base/ parent class is called using

Answer 7

super()

Question 8

super can be the last statement in the constructor of subclass (yes / no)

Answer 8

no, it must be the first statement in the subclass

Question 9

why does super class constructor must be called

Answer 9

to make sure all class members are initialized

Question 10

access modifier for an overriding method has to be the same ?

Answer 10

no it can be more but not less ( more access is given )

Question 11

if an access modifier protected then the child class can be ?

Answer 11

public or none

Question 12

any method defined in java is overridable by default unless it is ….

Answer 12

final

Question 13

method of subclass has the same signature of super class?

Answer 13

true

Question 14

method signture is

Answer 14

same name, same parameters and return type

Question 15

overloading is between methods

Answer 15

between methods of the same class

Question 16

same method name but different number of parameters or parameter type but not return type is considered overloading

Answer 16

true

Question 17

a class can have how many parent classes?

Answer 17

exactly one

Question 18

abstracted can not be …. or…..

Answer 18

inherited or instantiated

Question 19

a method declared abstract has no …

Answer 19

body

Question 20

abstract has to be

Answer 20

overridden

Question 21

abstract class can contain … classes

Answer 21

both concrete (non-abstract) and abstract

Question 22

constructors and static methods cant be declared abstract ? why?

Answer 22

yes , because they cant be inherited

we should call super for them to get invoked

Question 23

can an abstract class have a constructor ?

Answer 23

yes

Question 24

what happens if we try calling an abstract class constructor ?

Answer 24

compilation error

Question 25

if there at least one abstract method the class

Answer 25

the class must be abstract

Question 26

an abstract can be instantiated with a reference to any of its subclasses which is called an

Answer 26

upcasting 
parent name = new sub()

Question 27

polymorphism is

Answer 27

using methods to perform different tasks this allows us to perform a single action in different ways

Question 28

forms of polymorphism

Answer 28

overloading and overriding

Question 29

why polymorphism?

Answer 29

allows us to perform a single action in different ways

write general methods in super and implements them later in detail in subclasses

Question 30

dynamic binding

Answer 30

is making a thing change or overloaded

Question 31

dynamic binding happens in

Answer 31

runtime

Question 32

in dynamic binding the reference of an object is used? t or f

Answer 32

false

Question 33

dynamic binding speed is

Answer 33

low

Question 34

example for dynamic binding is

Answer 34

method overriding

Question 35

static binding happens in

Answer 35

compile time

Question 36

in static binding the … of an object is used

Answer 36

reference

Question 37

speed of static binding is

Answer 37

high

Question 38

static binding example is

Answer 38

overloading

Question 39

upcasting is

Answer 39

converting an object of a subclass to its superclass done implicitly (indirectly)

Question 40

downcasting is

Answer 40

converting an object of a superclass to one of its subclasses must be explicitly (directly)

Question 41

Upcasting example

Answer 41

Person p;
Employee emp = new Employee();
p = emp;

Question 42

DownCasting example

Answer 42

Person p = new Employee();
Employee emp;
emp = (Employee) p;

Question 43

instanceOf operator can be used to …

Answer 43

to check whether an object is a certain class type or not

Question 44

can you assign a superclass variable to superclass?

Answer 44

true

Question 45

can you assign a subclass variable to subclass object?

Answer 45

true

Question 46

can you assign superclass variable to a subclass object ?

Answer 46

true

Question 47

can you assign a subclass variable superclass object?

Answer 47

nope, must be done via explicit casting