Inheritance and interface

1
C.K.PITHAWALA COLLEGE OF
ENGINEERING & TECHNOLOGY, SURAT
Branch :- computer 3nd Year/5rd SEM (Div. D)
ALA Subject :- OOPJ
Topic Name :- Inheritance and interfaces
Group No :-B4
Enrolment No Name
Submitted To
160090107051
160090107049
160090107025
160090107044
160090107059
Shubham Sharma
Pakshal Shah
Hariom Maurya
Pravin Rathod
Naitik Vajani
Dr. Ami Choksi

Contents
 Introduction to inheritance
 Types of Inheritance
 Method overriding using inheritance
 Super keyword
 Final keyword
 Interfaces

Introduction to inheritance
 As the name suggests, inheritance means to take something that is already made.
 Inheritance is a unique feature of object oriented programming.
 Inheritance is mainly used for code reusability.
 The class which acquires the properties of the class is called as sub-class and the
class whose properties are acquired is called as superclass.
Consider the example:
As shown in example, the child inherit the properties of
father. Hence child will be subclass while father is a
superclass.

IS-A Relationship
 Inheritance defines IS-A relationship between a super class and its subclass
 For Example:
 Car IS A vehicle
 Bike IS A vehicle
 EngineeringCollege IS A college
 MedicalCollege IS A college
 In java, inheritance is implemented with the help of keyword - “extends”.

Types of inheritance
• Single inheritance
• Multilevel inheritance
• Hierarchical inheritance

Single Inheritance
 A structure having one and only one super class as well as subclass.
 Child class is authorized to access the property of Parent class.
Super class
Subclass
Syntax :
class A
{
………….
………….
}
class B extends A
{
………….
………….
}
Sharing of
properties

Multilevel inheritance
B
C
A
 When a class is derived from a class
which is also derived from a class, then
such type of inheritance is called as
multilevel inheritance.
Syntax :
class A
{
………….
………….
}
class B extends A
{
………….
………….
}
class C extends B
{
………….
………….
}

Hierarchical inheritance
 In hierarchical inheritance, one class is
inherited by many subclasses.
 subclasses must be connected with only
one super class.
B D
A
C
Syntax :
class A
{
………….
………….
}
class B extends A
{
………….
………….
}
class C extends A
{
………….
………….
}
class D extends A
{
………….
………….
}

Why multiple inheritance is not supported in java ?
 To reduce the complexity and simply the language, java doesn’t support
multiple inheritance.
 Suppose there are 3 classes A,B and C. The C class inherits class A and B.
 If A and B have same method and you call it from child class object, there
will be ambiguity to call method of A or B class.
 Since compile time errors are better than run time errors, java renders
compile time error if you inherit 2 classes.

Access Specifiers in java
 There are four Access Specifiers in Java
 1. Public: When a member of a class is declared as public specifier, it can be
accessed from any code.
 2. Protected: Protected is only applicable in case of Inheritance. When a
member of a class is declared as protected, it can only be accessed by the
members of its class or subclass.
 3. Private: A member of a class is declared as private specifier, can only be
accessed by the member of its class.
 4. Default: When you don't specify a access specifier to a member, Java
automatically specifies a default. And the members modified by default can only
be accessed by any other code in the package, but can't be accessed outside
of a package.

A program demonstrating inheritance in Java
1. class circle{
2. double radius;
3. void radius(double a)
4. {
5. radius=a;
6. }
7. double getdata()
8. {
9. double area;
10.area=3.14*radius*radius;
11.return area;
12.}
13.}
14.class cylinder extends circle{
15.double h;
16.void height(double b,double r)
17.{
18.radius=r;
19.h=b;
20.}
21.double getdata()
22.{
23.double volume;
24.volume=3.14*radius*radius*h;
25.return volume;
26.}

A program demonstrating inheritance in Java
27.public static void main(String[] args) {
28.cylinder c1=new cylinder();
29.c1.height(5.12,6.5);
30.double area,volume;
31.volume=c1.getdata();
32.System.out.println("Volume of cylinder :"+volume);
33.circle ob=new circle();
34.ob.radius(4.44);
35.ob.getdata();
36.area=ob.getdata();
37.System.out.println("area of circle:"+area);
38.}
39.}
Output of program:
Volume of cylinder :679.2447999999
Area of circle:61.90070400000001

Method overriding in Java
Subclasses inherit all methods from their superclass
Sometimes, the implementation of the method in the superclass does not
provide the functionality required by the subclass.
In these cases, the method must be overridden.
To override a method, provide an implementation in the subclass.
The method in the subclass MUST have the exact same signature as the
method it is overriding.

Program demonstrating method overriding
1. class A{
2. void display()
3. {
4. System.out.println("This is parent class.");
5. }
6. }
7. class B extends A{
8. void display()
9. {
10.System.out.println("This is first child class");
11.}
12.public static void main(String[] args) {
13.B b1=new B();
14.b1.display();
15.}
16.}
Output:
This is first child class

Super keyword
 As the name suggest super is used to access the members of the super class.
 It is used for two purposes in java.
1. The first use of keyword super is to access the data variables of the super class
hidden by the sub class.
 e.g. Suppose class A is the super class that has two instance variables as int a and
float b.
 class B is the subclass that also contains its own data members named a and b.
 Then we can access the super class (class A) variables a and b inside the subclass
class B just by calling the following command.
 super.member;

Super keyword
 2.Use of super to call super class constructor: The second use of the keyword
super in java is to call super class constructor in the subclass.
 This functionality can be achieved just by using the following command.
super(param-list);
 Here parameter list is the list of the parameter requires by the constructor in the
super class.
 super must be the first statement executed inside a super class constructor.
 If we want to call the default constructor then we pass the empty parameter
list.
 If we dont use super then the compiler does this task implicitly to instantiate
superclass members.

Program to demonstrate Super Keyword
1) class Animal{
2) Animal(){System.out.println("animal is created");}
3) }
4) class Dog extends Animal{
5) Dog(){
6) super();
7) System.out.println("dog is created");
8) }
9) }
10)class TestSuper3{
11)public static void main(String args[]){
12)Dog d=new Dog();
13)}}
Output:
Animal is created
Dog is created

Final Keyword
 The final keyword in java is used to restrict the user.
 The final keyword can be used in mainly 3 context.
1. Variable: If you make any variable final, you cannot change the
value of final variable.
Example:
1. class bike{
2. final int speedlimit=50;
3. void run(){
4. speedlimit=60; //Compile-time error
5. }
6. public static void main(String[] args){
7. Bike ob=new bike();
8. ob.run();
9. }
10. }
Output:
Compile time error

Final keyword
2. Method: If you make a method final, you cannot override it.
Example:
1. class bike{
2. final void run(){
3. System.out.println(“Running”);
4. }
5. class honda extends run(){
6. void run(){ //compile time error
7. System.out.println(“Running at 100 kmph”);
8. }
9. }
11. Bike ob=new bike();
12. ob.run();
13. }
14. }
Output:
Compile time error

Final keyword
3. Class : If you make any class final, you cannot extend it.
Example:
1. final class bike{
2. //code here
3. }
4. class honda extends run(){ //Compile time error
5. void run(){
6. System.out.println(“Running at 100 kmph”);
7. }
9. honda ob=new honda();
10. ob.run();
11. }
12. }
Output:
Compile time error

Interface in Java
 Java Supports a special feature called interface.
 This feature helps to connect a class with more than
one classes (in order to achieve multiple inheritance).
 For this type of connectivity java uses ‘implements’
keyword.
 A class can implements multiple interfaces at a same
time
 All the variables defined in the interface are final and
cannot be changed in subclass.
Syntax :
interface A
{
int a=10;
public int getdata();
public void display();
}
interface B
{
public void getmarks();
}
class D implements A,B
{
………..
………..
}

Comparison between interface and abstract class
Features Interface Abstract class
Multiple inheritance A class may implement
multiple interfaces
A class can extend only one
abstract class
Default implementation An interface cannot provide
any code at all
An abstract class can
provide complete code,
default code
Constants Constants are by default
Static and final
Both static and instance
constants are allowed
Object An object of interface is
never created
An object of abstract class
can be created

Program demonstrating interfaces
1. interface Printable{
2. void print();
3. }
4. interface Showable{
5. void show();
6. }
7. class A7 implements Printable,Showable{
8. public void print(){System.out.println("Hello");}
9. public void show(){System.out.println("Welcome");}
10.public static void main(String args[]){
11.A7 obj = new A7();
12.obj.print();
13.obj.show();
14. }
15.}
Output:
Hello
Welcome

Inheritance and interface

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Inheritance and interface