inheritance

Inheritance

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Define

● Deriving new classes from existing classes such that the new classes acquire all the features of existing classes is called inheritance


How

● Use of keyword extends

A

B<extends>

class A{

- - - - - -- - -

}

class B extends A{

- - - - - -- - -

}

Super Class

Sup Class


Types of Inheritance in Java

● Multilevel Inheritance

AB

● Simple Inheritance

C

A

B C. . .


Why ????

● Why NO to multiple Inheritance in Java ?

Dimond Problem A

B C

D


Multiple Inheritance

A

B C


NOTE

“When SUB Class object is created , first of all the super class default constructor is called and then only SUB class constructor is called”


From SubClass To SuperClass

● Private Members not accessible from SubClass

● From SubClass object we can access the SuperClass methods and properties

● From SuperClass object we can not access the SubClass methods and properties


A

B

B b new B( )=

Reference of Sub Class

Object of Sub Class

<extends>

SUB:SUB

<access>

<access>


A

B

A a new A( )=

Reference of SUPER Class

Object of SUPER Class

<extends>

SUPER:SUPER

<access>


Protected Specifier

● It is commonly used in SUPER class to make the member of the SUPER class available directly in its SUB class.


Overriding

● An instance method in a SUB class with the same signature and return type as an instance method in the SUPER class overrides the superclass's method


SUB:SUB[Method:Override]

A

B

B b new B( )=

Reference of Sub Class

Object of Sub Class

<extends>

<access> <CAT>

<access> <CAT>


Rules for Overriding

● Argument and return type must be same ● A final method can not be overridden● A method declared static cannot be override● If a method cannot be inherited , then it cannot

be override● Constructors cannot be override


Run Time Polymorphism

● It is also called as dynamic polymorphism

A

B

C

A a

A a

A a

= new A( )

= new B( )

= new C( )

a.

i)

ii)

iii)


Overloading vs Overriding

● Overloading– Static/Compile time

Polymorphism

– JVM decides which method is called depending on the difference in the method signature

– It is done in same class

– Method return type can be same or different

● Overriding– Dynamic/Run Time

Polymorphism

– JVM decides which method is called depending on the data type of the object used to calls

– It is done in SUPER and SUB class

– Method return type should also be same


super

● From SUB class object we can access the super class methods and properties

● Use of super :-– If we have same names of member in SUB as in

SUPER class then SUB members are accessible

– Invoke SUPER class constructor


final

● Final Methods– Methods declared final are called final methods

– NO to overriding : As : NOT available to SUB class

– When we wish that its implementation should not be changed

● Final Class– NO to SUB class : NO to inheritance


Type Casting


A

B

A a new B( )=


Object of SUB Class

<extends>

Exclusive:Methods[Widening/Generalization]


A

B

A a new B( )=


Object of SUB Class

<extends>

Override:Methods[Widening/Generalization]


A

B

B b new A( )=

Reference of Sup Class

Object of Super Class

<extends>

Exclusive:Methods[Narrowing:Specialization]


A

BA aB b

new B( )(B) a

=



<extends>

Exclusive:Methods[Narrowing:Specialization]

=


A

BA aB b

new B( )(B) a

=



<extends>

Override:Methods[Narrowing:Specialization]

=


Type Casting Referenced Data Type

ParentGeneralization/Downcasting

Specialization/Upcasting

* study in detail after inheritence

inheritance

Engineering