This document discusses interfaces in Java. It defines an interface as a collection of public abstract methods and public static final variables that defines a protocol for classes to implement but cannot be instantiated itself. Interfaces allow for multiple inheritance and reveal functionality without implementation details. The document explains how to define an interface with the interface keyword and how classes implement interfaces by matching method signatures. It also covers key properties of interfaces like default access modifiers and differences between interfaces and abstract classes. Benefits of interfaces include allowing standard method sets across hierarchies and resilience to class changes.

1. Chameli Devi School Of Engineering, Indore
FTP
ON
Interface
Presented By
Shantilal Bhayal

2. Content
 What is Interface.
 Why use Interface.
 How Define interface.
 How use Interface.
 Key Points for Interface.
 Abstract Class Vs Interface.
 Benefit Of Interface.

3. What is an Interface
 Interface looks like class but it is not a class.
 It is a Collection of :
1. Public and Abstract method.
2. Public ,static and final variables.
 Cannot be instantiated. Only classes that implements interfaces can be
instantiated.
 Protocol for classes that completely separates specification/ behaviour
from implementation.

4. Why use Interface
1. To model multiple inheritance .
2. To have unrelated classes implements similar methods(behavior).
Example:
Class Line and class MyInteger
Interface:
checkIsGreater(Object x, Object y)
checkIsLess(Object x, Object y)
checkIsEqual(Object x, Object y)
3. To reveal an object's programming interface (functionality of the
object) without revealing its implementation

5. How define Interface
 An interface is defined much like a class but using interface keyword.
 Syntax :
access modifier interface Interface_name
{
return-type method-name1(parameter-list);
return-type method-name2(parameter-list);
type varname1 = value;
type varname2 = value;
// ... return-type method-nameN(parameter-list);
type final-varnameN = value;
}

6. How use Interface
 Once an interface has been defined, one or more classes can
implement that interface.
 Syntax:
access_modifier class classname implements interface1,
interface2….interfaceN
{
// class-body
}
 Type signature of the implementing method must match exactly
the type signature specified in the interface definition.

7. Key Points about Interface
 We can’t instantiate an interface in java.
 All the interface methods are by default abstract and public.
 Variables declared in interface are public, static and final by
default.
 Interface variables must be initialized at the time of declaration
otherwise compiler will through an error.
 Any interface can extend any other interface but cannot
implement it.

8. Key Point Continued…
 Variable names conflicts can be resolved by interface name
interface A
{
int x=10;
}
interface B
{
int x=100;
}
class Hello implement A,B
{
public static void Main(String arg[])
{
System.out.println(x); // reference to x is ambiguous both variables are x
System.out.println(A.x);
System.out.println(B.x);
}
}

9. Continue..
 A class can implements any number of interfaces.
 Interface cannot be declared as private and protected .
 Class implementing any interface must implement all the
methods, otherwise the class should be declared as “abstract”.
 While providing implementation in class of any method of an
interface, it needs to be mentioned as public.
 Inside any implementation class, you cannot change the
variables declared in interface.

10. Interface Abstract Class
1 All methods in interface are by
default Abstract.
Abstract class can have Abstract as
well as concrete Methods.
2 Variables declared in interface is
by default final
An abstract class may contain non-final
variables
3 Members of a Java interface are
public by default
A Java abstract class can have the
usual flavors of class members like
private, protected, etc
4 Interface do not have
Constructors
Abstract class can have
Constructors
5 Multiple inheritance possible Multiple inheritance not
possible

11. Benefits of Interface
 Provide multiple inheritance.
 Allow standard sets of methods to be used across the class
hierarchy.
 As interfaces are declared independently of classes, they are
unaffected by changes to specific classes.

12. Drawback of Interfaces
 Interfaces cannot grow.
 Cannot add more methods to the existing interface.
 One has to re-implement all the classes which implements
the interface when it grows.

13. Thank You