Inheritance allows subclasses to inherit and extend the functionality of parent classes. The example code shows inheritance being used to create subclasses for different employee types (Engineer, Manager, SalesManager) that inherit from a base Employee class. The subclasses override the printData() method to print employee-specific pay details while reusing common functionality like name printing from the parent class. This avoids duplicating code and allows adding new functionality through inheritance.

1. Chapte
r
Thre
e
Inheritan
ce u
1
0

2. What Is Inheritance?
In the real world: we inherit traits from our
motheran
d
father
.
We als
o
inherit traits from
We
our
migh
t
grandmothe
r,
grandfathe
r,
an
d
ancestor
s.have similar eyes, the
same
smile,A different
height.
But we are in many ways "derived" from our
parents.
In software: object inheritance is more well
defined!
Objects that are derived
from
other
both
object
"resemble"their parent
s
by inheritin
g
stat
e
(fields
)
an
dbehavior
(methods). 2
uu )

3. Contd
.Inheritanc
e
is A fundament
al
featur
e
of object-
orientedprogrammin
g
whic
h
enable
s
the
programmer
to write A
class based on an already existing
class.
Th
e
already existin
g
clas
s
is calle
d
the paren
t
clas
s,
or
orsuperclas
s,
and the ne
w
clas
s
is calle
d
the subclas
s,derived
class.
Th
e
subclass
inherits
(reuse
s)
the no
n
private member
s(methods and variables) of
the
its own members as well.
superclass, and may
define
Inheritance
extends.
 When class b is a subcla
uss o
uf class a, we say b
is
implemented
in java usin
g
the keywor
d
3
)

4. Advantages Of
Inheritance.Cod
e
reusabilit
y:-
inheritan
ce
automates the
process
of
reusing the code of the superclasses in the
subclasses.
 With inheritance, an object can inherit its more general properties
from its
paren
t
object
,
and that save
s
th
e
redundanc
y
in
programmin
g.
Cod
e
maintenan
ce:-
organizin
g
cod
e
int
o
hierarchic
alclasses makes its maintenance and management
easier.
Implement
ing
OOP:-
inheritance
help
s
to impleme
nt
th
ebasic oop philosophy to adapt computing to the
problem
and not the other way around, because entities
(objects)
in the real world are often organized into a
hierarchy.
4
uu )

5. Inheritance
TypesA.
Single
level
inheritance:-
inheritance
in
super class.
which a
class inherits from only
one
B. Multi-
level
inheritance:
-
inheritanc
e
in which a
class inherits from a class which itself inherits
from
another class.Here a minimum of
three
classes is
required.
here two or more

C. Hierarchy
inheritance:-
inherits from one class.
D. Multiple inheritance:-
a
more classes.
classe
s
class inherits
from
two or
This type of inheritance is not supported in
java.

5
)

6. Dog
Class
public class Dog {
private String name;private int fleas;
public Dog(string n, int f) {
name =
fleas =
n;
f;
}
public
public
public
String getName() { return name; }
int getFleas() { return fleas; }
void speak() {
System.out.println("woof");
}
} 6
uu )

7. CAT
CLASSpublic class Cat {
private string name;
private int hairBalls;
public Cat(string n, int
name = n;
hairballs = h;
}
h) {
public
public
public
String getName() { return name; }
int getHairBalls() { return
void speak() {
hairballs; }
System.out.println("meow");
}
} 7
uu )

8. Problem: Code
Duplication
Dog and Cat have the name field and
the
getName method in common
Classes
often
in common
have a lot of
state
and behavio
r
Resul
t:
lot
s
of duplicate
code!
8
uu )

9. Solution:
Inheritance
Inheritance allows you to write new classes that
inherit
from existing classes
The existing class whose properties are inherited is
called
the "parent" or superclassThe new class that
inherits
the "child" or subclass
Result: lots of code
reuse!
from the supe
r
clas
s
is calle
d
9
uu )

10. using
inheritance
superclass
subclass
subclass
10
)
Dog
int fleas int
getFleas()
void speak() uu
Cat
int hairballs int
getHairballs()
voidspeak()
Animal String
name String
getName()
Cat String
name int
hairballs
String getName()
int getHairballs()
voidspeak()
Dog String
name int
fleas
String getName()
int getFleas()
void speak()

11. Animal
Superclass
public
{
class Animal
private String name;
public Animal(string n) {
name = n;
}
public String getName() {
return name;
}
}
11
uu )

12. Dog
Subclass
public class Dog extends Animal {
private int fleas;
public Dog(string n, int f) {
super(n); // calls animal
fleas = f;
constructor
}
public int getFleas()
return fleas;
}
{
public void speak() {
return System.out.println("woof");
}
uu
} 12
)

13. Cat
Subclass
public class Cat extends Animal {
private int hairballs;
public Cat(string n, int h) {
super(n); // calls animal
hairballs = h;
constructor
}
public int getHairBalls() {
return hairballs;
}
public void speak() {
return System.out.println("meow");
}
} 13
uu )

14. Inheritance
Quiz
1
• What is the output of the
following?Dog d
Cat c
=
=
new Dog("rover" 3);
new Cat("kitty", 2);
System.out.println(d.getName() + " has " +
d.getFleas() + " fleas");
System.out.println(c.getName() + " has " +
c.getHairBalls() + " hairballs");
rover has 3 fleas
kitty has 2
hairballs
14
(Dog and Cat inherit the ge
utN
uame method from
)

15. Inheritance
Rules
Us
e
the extends keyword to indicat
e
that one clas
sinherits from another
The subclass inherits all the nonprivate fields and
methods of the superclass
Use the super keyword
in
the subclas
s
constructor to cal
lthe superclas
s
constructor
15
uu )

16. Subclass
Constructor
• The first thing a subclass constructor must do is
call
the superclass constructor.
• This ensures that the superclass part of the
object is
constructed before the subclass part
• If you do not call the superclass constructor with
the super keyword, and the superclass has a
constructor with no arguments, then that
superclass
16
uu )

17. Implicit Supe
r
Constructor
Call
then this Beef subclass:
public class Beef extends Food
private double weight;
public Beef(double w) {
weight = w
}
}
{
if I have this food
class:
public class food
{
private boolean
public food() {
raw = true;
}
}
raw;
is equivalent to:
public class Beef extends Food
private double weight;
public Beef(double w) {
super();
weight = w
{
17
}
u}u )

18. Inheritance Quiz
2public class
public A()
}
A
{
{
System.out.println("I'm A"); }
public class
public B()
}
B
{
extends A {
System.out.println("I'm B"); }
public class
public C()
}
C
{
extends B {
System.out.println("I'm C"); }
What does this print out? I'm
I'm
I'm
A
B
CC x = new C(); 18
uu )

19. Overriding
Methods When a
method
type signature
as
method is said
to
in a super class has the same name as
and
a method in the superclass, then the
subclass
override the method in the superclass.
 During overriding a method the following takes place:
 The new method overrides (and hides) the original
method.
 When you override a method, you can call the
superclass's
copy of the method by using the syntax
super.method().
 You can not do super.super. to back up two levels.
 You canno
t
chang
e
the return type whe
n
overridin
g
impossibl
e.
a
method, since this would make
polymorphism
uu )

20. class MyDerived extends
{
int y;
MyBase
class MyBase
{
private int
public MyDerived(int
{
super(x);
}
public MyDerived(int
{
super(x);
x)
x;
public MyBase(int
{
x)
x, int y)
this.x
}
= x;
public
{
return
}
public
{
int getX()
this.y
}
public
{
return
}
public
{
= y;
x;
int getY()
void show()
y;
System.out.println("x="
}
}
+ x);
void show()
super.show();
System.out.println("y = " + y);
} 20
uu}
)

21. Final Variables, Methods
And
Class
es All methods and
variables
in subclasses.
can be overridden by
default

Use
th
e
fin
al
keywor
d
member
s
to
of
preven
t
th
e
subclass
es
from
overriding
the
Example:
final
th
e
superclas
s. This method
will not be
overridden
int num=10;
public final void show()
{
System.out.println("x=" +
}
x);
 It is also possible to define a class as final
if we
class not to be inherited.
 Any attempt to inherit a final class will
cause
wan
t
th
e
an
error 21
)

22. Abstract Classes
An abstract method is a method that is declared
without implementation .
an
Exampl
e:
abstract void display();
An abstrac
t
clas
s
is a clas
s
that is incomplet
e,
or to be
considered incomplete.
Only abstract classes may have abstract
methods, that
is
,

methods that are declared but not yet implemented
and non
abstract methods.
An abstract class may or may not contain abstract
methods.
An abstract class is a class that cannot be
instantiated, we


cannot create instances of
uan
uabstract
22
)

23. Contd.
While using abstract classes:
 We cannot use abstract
classes
directly.
to instantiate
objects

The
abstract method
of
an
abstract
clas
s
mus
t
be
defined in its
subclass.
 We cannot
declare
abstract constructors
or
abstrac
tstatic methods.
 Abstract classes
can
methods and one
or
have none, one or
more
abstrac
tmore non abstract
methods. 23
)

24. abstract class A
{
abstract void callme(); // abstract method
void callmetoo() // Non-abstract method
{
System.out.println("This is a concrete method.");
}
}
class B extends A
{
void callme() //Implementation of super class’s
{
abstract method
System.out.println("B's implementation of callme.");
}
}
class AbstractDemo
{
public static void main(String args[]) {
A
A
B
ab;// possible
ab1=new A();
b = new B();
// Is not correct
b.callme();
b.callmetoo(); 24
uu}
}
)

25. Visibility Control (Access Level)
 By using inheritance it is possible to inherit all members
of the superclass being on the subclasses.
 But it is also possible to
restrict
from outside the class. This s
done
the access of certain
fields
using access modifiers.

Classes
can contain
fields
and method
s
of four different
access
levels:
A.
private:-
private variable
s
and method
s
are accessibl
ewithin their own class (access only to
the class
itself)
.
B. Friendly access:- when no access modifier is
specified, themembers’ are access only to classes in
the same
No access level is specified in this
case.
package
.
25
)

26. Contd.
C. protected:- makes the fields visible to all
classes andsubclasses
within
th
e
sam
e
package and
to
all
subclasses from other
packages.
D.
Private
protecte
d:-
make
s
th
e
fields visible
in
all
subclasses regardless of what package they
are in.
These fields are not accessible by other
classes in
the same package.
E. public:- These variables or methods have
access to all
classes everywhere.
26
such
members.
u
))

27. Programming Example
A company has a list of employees. It asks you to
provide a
payroll sheet for all employees.
Has extensive data (name, department,
pay
employees.
amount, …) for
all
Different types
engineer.
You have an old employee class but
need to
of employee
s
– manager
,
enginee
r,
softwar
e
add very different
data and methods for managers and
engineers. Suppose
someone
wrote a nam
e
syste
m,
and already
provided a legacy employee class.
 The old employee class had a printData()
method
for
eachemployee that only printed the name. We want to reuse
it, and
27
uuprint pay
info. )

28. Review
PictureMessage passing "Main event loop"Encapsulation
Employee e1
private:
lastName
firstName
uu )
printData
public … Main(…){
Employee e1…("Mary","Wang");
...
e1.printData();
// Prints Employee names.
...
}
28

29. Employee
class
//This is a simpler super class
class Employee {
// Data
private String firstName, lastName;
// Constructor
public Employee(String fName, String lName) {
firstName= fName; lastName= lName;
}
// Method
public void printData() {
System.out.println(firstName + " " + lastName);}
}
29
uu )

30. Inheritance
Diagram
Already written:
Class Employee printData()firstName
lastName
is-a
Class Engineer
is-a
Class Manager
firstName
lastName
firstName
lastName
hoursWorked
salary
wagesprintData()
getPay()
printData()
getPay()
30
You
une
uxt write:
)

31. Engineer Class
//A subclass derived from Employee class
class Engineer extends Employee {
private double wage;
private double hoursWorked;
public Engineer(String fName, String lName,
double rate, double
super(fName, lName);
wage = rate;
hoursWorked = hours;
hours) {
}
public double getPay() {
return wage * hoursWorked;
}
public void printData() {
super.printData();
System.out.println("Weekly
uu
// PRINT NAME
pay: Birr" + getPay();
31
}
}
)

32. Manager
Class
//A subclass derived from Employee class
class Manager extends Employee {
private double salary;
public Manager(String fName,
super(fName, lName);
salary = sal; }
String lName, double sal){
public double getPay() {
return salary; }
public void printData() {
super.printData();
System.out.println("Monthly salary: Birr" + salary);}
}
32
uu )

33. Inheritance
…
Class Manager
firstName
lastName
is-a
Salary
Class SalesManager
firstName
lastName
Salary
getPay
u
33
u salesBonus
)
printData
printData
getPay

34. Sales Manager
Class
//A subclass derived from Manager class
class SalesManager extends Manager {
private double salesBonus;
commission.
// Bonus Possible as
// A SalesManager gets a constant
public SalesManager(String fName,
super(fName, lName, 1250.0);
salesBonus = b; }
salary
String
of $1250.0
lName, double b) {
public double getPay() {
return 1250.0; }
public void printData() {
super.printData();
System.out.println("Bonus Pay:
uu
$" + salesBonus; }
34
}
)

35. Main
Method
public class PayRoll {
public static void main(String[] args) {
// Object creation and Initialization (Using constructors)
Engineer fred
Manager ann
= new Engineer("Fred", "Smith", 12.0, 8.0);
= new Manager("Ann", "Brown", 1500.0);
SalesManager mary= new SalesManager("Mary", "Kate", 2000.0);
// Polymorphism, or late binding
Employee[] employees = new Employee[3];
employees[0]=
employees[1]=
employees[2]=
fred;
ann;
mary;
System.out.println(“===========================“);
for (int i=0; i < 3; i++)
employees[i].printData();
System.out.println(“===========================“);
}
uu
35
}
)

36. Output from Main
===========================
Fred Smith
Weekly pay: $96.0
Ann Brown
Monthly salary: $1500.0
Mary Barrett
Monthly salary: $1250.0
Bonus: $2000.0
===========================
Note that we could not write:
employees[i].getPay();
Method
becaus
e
getPay(
)
is no
t
a metho
d
of th
e
supercla
ssEmployee.
In contrast, printData() is a
method of
can find the appropriate version.
Employee, so
Java
36
)

37. Object Class
All java classes implicitly inherit from
java.lang.Object
So every class you write will automatically have
methods in
object such as equals, and toString etc.
We'll learn
about
the importanc
e
of som
e
of thes
e
methods
inlater lectures
.
37
uu )