Abstract n Interface &

8/8/2019 Abstract n Interface &

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ABSTRACTCLASS &

JAVAINTERFACE


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Abstract Classes

OBJECTIVESu

What is an Abstract method?

Abstract class?

When to use???

Exaples.

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Abstract method:

Keyword abstractis used.

abstracttype name(parameter-list);

When to use Abstract Methods &Abstract Class?

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Abstract Classes


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Example

// A Simple demonstration of abstract.

abstract class A {

abstract void callme();

// concrete methods are still allowed inabstract classes

void callmetoo() {

System.out.println("Th

is is a concretemethod.");

}

}4


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class B extends A {

void callme() {

System.out.println("B's implementation ofcallme.");

}

}

class AbstractDemo {

public static void main(String args[]) {

B b = new B();

b.callme();

b.callmetoo();

}

} 5


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// Using abstract methods and classes.abstract class Figure {

double dim1;

double dim2;Figure(double a, double b) {

dim1 = a;

dim2 = b;

}

// area is now an abstract method

abstract double area();

} 6

Example 2


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class Rectangle extends Figure {

Rectangle(double a, double b) {

super(a, b);}

// override area for rectangle

double area() {

System.out.println("Inside Area for

Rectangle.");

return dim1 * dim2;

}}

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class Triangle extends Figure {

Triangle(double a, double b) {

super(a, b);}

// override area for right triangle

double area() {

System.out.println("Inside Area for Triangle.");

return dim1 * dim2 / 2;

}

}

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class AbstractAreas {

public static void main(String args[]) {

// Figure f = new Figure(10, 10); // illegal nowRectangle r = new Rectangle(9, 5);

Triangle t = new Triangle(10, 8);

Figure figref; // this is OK, no object is created

figref = r;

System.out.println("Area is " + figref.area());

figref = t;

System.out.println("Area is " + figref.area());}

}

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Interfaces

OBJECTIVESu

Defining an Interface

Implementing an Interface Implementing multiple Interface's

Inheritance among Interface's

Interface and Polymorphism Rewriting an Interface

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interface InterfaceName

{

variables declaration;

methods declaration;

}

Variables declared as:

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Interfaces

Static final type VariableName = value;


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interface Driveable

{

boolean startEngine( ) ;void stopEngine( ) ;

float accelerate( float acc ) ;

boolean turn( Direction dir ) ;}

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Example


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IMPLEMENTING INTERFACES:

class classname [extends superclass]

[implements interface1[,interface2]]

{

//class body

}

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class Automobile implements Driveable{

...

public boolean startEngine( )

{

if ( notTooCold )

engineRunning = true;

...

}

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Example


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public void stopEngine( )

{

engineRunning = false;

}

public float accelerate( float acc ){

...

}

public boolean turn( Direction dir ) {

...}

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After declaring the interface, we have a new

type, Driveable.We can declare variables of

type Driveable and assign them any instance

of a Driveable object:Automobile auto = new Automobile( );

Lawnmower mower = new Lawnmower( );

Driveable vehicle;

vehicle = auto;

vehicle.startEngine( );

vehicle.stopEngine( );

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Interface as a type


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Reason 1:

To reveal an object's programming interface

(functionality of the object) without revealing its

Implementation

Reason 2:

To have unrelated classes implement similar

methods (behaviors)

Reason 3:

To model multiple inheritance - you want to impose

multiple sets of behaviors to your class17

Why interfaces???


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//one interface can extend another.Interface A{

void meth1( );

void meth( )2;

}

//B now includes meth1( ) and meth2( )---- it adds

meth3( )

Interface B extends A {

Void meth3( );

}

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Interfaces can be extended


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//This class must implement all of A and B

Class MyClass implements B {

public void meth1( ){

System.out.println(Implement meth1( ));

}

public void meth2( ){

System.out.println(Implement meth2( ));

}

public void meth3( ){System.out.println(Implement meth3( ));

}

}


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Class IFExtend {

Public static void main(String arg[ ] ) {

Myclass ob = new Myclass ( ) ;

Ob. meth1( ) ;

Ob. meth2( ) ;

Ob. meth3( ) ;

}

}


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BY:

VISHEKHACHATURVEDI

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