polymorphism

Question 1

define polymorphism

Answer 1

ability to associate many meanings to one method name - late binding is used to do so

Question 2

difference between inheritance and polymorphism

Answer 2

inheritance allows a base class to be defined and in other classes derived from it - code from base classes can then be used for its own and derived objects

polymorphism allows changes to be made to the method definitions in the derived classes and have those changes appled to the software written for the base class

Question 3

what is BINDING

Answer 3

process of associating a method definition with a method invocation

Question 4

what is early binding

Answer 4

if the method definition is associated with its invocation when the code is actually compiled

Question 5

what is late binding

Answer 5

if the method definition is associated with its invocation when the method is invoked at run time

Question 6

java uses late binding for all methods except…

Answer 6

private
static
final

Question 7

because of late binding a method can be written in a base class to perform a task even if

Answer 7

portions of that task aren’t defined yet

Question 8

static binding

Answer 8

when the decision of which definition of a method to use is made at compile time

this decision is made based on the type of the variable naming object

Question 9

when does java use static binding

Answer 9

private
static
final

late binding for private and final would make no difference - it does make a difference in static methods

Question 10

what does the final keyword mean

Answer 10

no sub-classes can be made

this method cannot be overridden

Question 11

expand the statement: an object knows the definitions of its methods

Answer 11

the type of class variable determines which method names can be used with the variable

however, the object names by the variable determines which definition with the same method name is used

Question 12

what is the special case of the rules mentioned above?

Answer 12

the type of a class parameter determines which method names can be used with the parameter
the argument determines which definition of the method name is used

Question 13

define upcasting

Answer 13

when an object of a derived class is assigned to a variable of a case class or any ancestor class

• late binding occurs
  e. g. discount sale into a sale

Question 14

what is downcasting

Answer 14

when a type cast is performed from a base class to a derived class (or from any ancestor or descendent class)

Question 15

pitfalls with downcasting

Answer 15

must be done very carefully
cant put a specialized object into a general object
can only be done when you know for sure that the general object can actually fit into the derived class

e.g. sale into a discount sale

Question 16

how to do downcasting

Answer 16

Sale otherSale = Sale(otherObject)

Question 17

how to check if downcasting is legitimate

Answer 17

downcasting to a specific type is only sensible if the object being cast is an instance of that type – use the instance of

Question 18

what does instanceof return

Answer 18

returns true if object is of class type or if object is an instance of any descendent class

Question 19

where does every object inherit a clone method from

Answer 19

class Object

Question 20

what does clone do

Answer 20

returns a deep copy of the calling object -each class must override it

Question 21

define covariant return types

Answer 21

google it

Question 22

invoking the clone method

Answer 22

Sale copy = orginalObj.clone()

Sale copy = (Sale)original.clone();

Question 23

when must you use the clone method

Answer 23

when dealing with inheritance

Question 24

what are the limitations of copy constructors

Answer 24

polymorphism doesnt work with methods of different names - you will loose the fact that the Sale is a DiscountSale

Question 25

what is an abstract class

Answer 25

“postpone the definition of a method until we know the exact type that that method needs to work on”

In order to postpone the definition of a method, Java allows an abstract method to be declared
An abstract method has a heading, but no method body
The body of the method is defined in the derived classes
The class that contains an abstract method is called an abstract class

Question 26

What is a concrete class

Answer 26

a class that has no abstract methods

Question 27

can you create instances of abstract classes?

Answer 27

no  - abstract classes can only be used to derive more specialized classes 
abstract class constructor cannot be used to create an object of the abstract class - however in a derived class the constructor will include an invocation of the abstract class constructor in the form of super

Question 28

can you have an abstract class as a parameter

Answer 28

Although an object of an abstract class cannot be created, it is perfectly fine to have a parameter of an abstract class type
-This makes it possible to plug in an object of any of its descendent classes

It is also fine to use a variable of an abstract class type, as long is it names objects of its concrete descendent classes only