Embed Size (px)
Citation preview
Interface in JAVAInterface in JAVA
Presented By :Presented By : Mr. Dheeraj Kumar Singh Assistant Professor I.T. Department, Faculty of Engg., Parul
University, Vadodara, Gujarat
OutlineOutline Introduction to Interface Multiple Inheritance – Example Why Interfaces are needed Java's Interface Concept Syntax Semantic Rules for Interfaces Example: An Interface for Shape Classes Extending Interface Abstract class and Interface Benefits of Interfaces Java's Most used Interfaces
2
IntroductionIntroduction toto InterfaceInterface
3
In General, An interface is a device or system that unrelated entities use to interact. - The English language is an interface between two people.- A remote control is an interface between you and a television.
IntroductionIntroduction toto InterfaceInterface
4
In Computing, An interface is a shared boundary across which two or more components of a computer system exchange information.
- The exchange can be between software, hardware, humans and combinations of these.
Interface/Medium
5
In Object oriented programming,
- An interface is a common means for unrelated objects to communicate with each other.
In Java,
- An interface is a way through which unrelated objects use to interact with one another.
- Using interface, you can specify what a class must do, but not how it does it.
- It is not a class but a set of requirements for classes that implement the interface
IntroductionIntroduction toto InterfaceInterface
Multiple Inheritance Multiple Inheritance - Example- Example
departmentcgpa()
Studentdepartment
salary()
Employee
Person Name
displayDetail()
TeachingAssistantTeachingAssistant
For a teaching assistant, we want the properties from both Employee and Student.
6
Problems with Multiple InheritanceProblems with Multiple InheritanceConsider following declearation:
ta = new TeachingAssistant(); ta.department;
Name clash problem: Which department does ta refers to?Combination problem: Can department from Employee and Student be combined in Teaching Assistant? Selection problem: Can you select between department from Employee and department from Student? Replication problem: Should there be two departments in TeachingAssistent?
7
Why Interfaces are neededWhy Interfaces are needed
• Multiple Inheritance in JAVA is not allowed – cannot extend more than one class at a time.
• An object may need IS-A relationships with many type.
Politician
Citizen
Father
President
8
Solution for multiple inheritance in Solution for multiple inheritance in JAVAJAVA
public class Person extends Citizen implements Father, Politician, President {}
public interface Politician {public void joinParty();
}
public class Citizen {}
public interface Father {public void care();
}
public interface President {public void winPoll();
}
public class Person {} 9
10
• An interface defines a protocol of behavior as a collection of method definitions (without implementation) and constants, that can be implemented by any class.
• A class that implements the interface agrees to implement all the methods defined in the interface.
• If a class includes an interface but does not implement all the methods defined by that interface, then that class must be declared as abstract.
Java's Interface Concept
SyntaxSyntaxThe Declaration of Interface consists of a keyword interfaceinterface, its name, and the members.interface InterfaceName {// constant declarationstatic final type variableName = value;// method declarationreturntype methodname (argumentlist);}The Class that Implements Interface called as Implementation Class uses keyword implementsimplements:class classname implementsimplements InterfaceName {... }
11
12
• InstantiationDoes not make sense on an interface. Interfaces are not classes. You can never use the new operator to instantiate an interface.
public interface Comparable {. . . }
Comparable x = new Comparable( );• Data Type
An interface can be used as a type, like classes. You can declare interface variables
class Employee implements Comparable {. . . }Comparable x = new Employee( );
Semantic Rules for InterfacesSemantic Rules for Interfaces
13
• Access modifiers
An interface can be public or “friendly” (default).
All methods in an interface are by default abstract and public.
- Static, final, private, and protected cannot be used.
All variables (“constants”) are public static final by default
-Private, protected cannot be used.
Semantic Rules for InterfacesSemantic Rules for Interfaces
14
Example: An Interface for Shape Example: An Interface for Shape ClassesClasses
• Creating classes to represent rectangles, circles, and triangles and compute their area and perimeter
It may seem as there is an inheritance relationship here, because rectangle, circle, and triangle are all shapes.
But code sharing is not useful in this case because each shape computes its area and perimeter in a different way.
15
Define Interface ShapeDefine Interface Shape
• A better solution would be to write an interface called Shape to represent the common functionality (to compute an area and a perimeter ) of all shapes:
public interface Shape { public double getArea(); public double getPerimeter();}
16
Class Rectangle implements Class Rectangle implements interface Shape interface Shape
public class Rectangle implements Shape { private double width; private double height; // Constructs a new rectangle with the given dimensions. public Rectangle(double width, double height) { this.width = width; this.height = height; } // Returns the area of this rectangle. public double getArea() { return width * height; } // Returns the perimeter of this rectangle. public double getPerimeter() { return 2.0 * (width + height); }}
17
Class Circle implements interface Class Circle implements interface ShapeShape
public class Circle implements Shape { private double radius; // Constructs a new circle with the given radius. public Circle(double radius) { this.radius = radius; } // Returns the area of this circle. public double getArea() { return Math.PI * radius * radius; } // Returns the perimeter of this circle. public double getPerimeter() { return 2.0 * Math.PI * radius; }}
18
Class Class Triangle Triangle implements implements interface Shapeinterface Shape
public class Triangle implements Shape { private double a; private double b; private double c; // Constructs a new Triangle given side lengths. public Triangle(double a, double b, double c) { this.a = a; this.b = b; this.c = c; } // Returns this triangle's area using Heron's formula. public double getArea() { double s = (a + b + c) / 2.0; return Math.sqrt(s * (s - a) * (s - b) * (s - c)); } // Returns the perimeter of this triangle. public double getPerimeter() { return a + b + c; }}
Class Class Mensuration with Main Mensuration with Main FunctionFunction
class Mensuration{public static void main (String [] arg){// Rectangle object Rectangle r = new Rectangle(10,20); // Rectangle object System.out.println("Area of Rectangle =" +(r.getArea()));System.out.println("Perimeter of Rectangle =" +(r.getPerimeter()));Circle c = new Circle(10); // Circleobject System.out.println("Area of Circle =" +(c.getArea()));System.out.println("Perimeter of Circle =" +(c.getPerimeter()));Triangle t = new Triangle(3,4,5); // Triangle object System.out.println("Area of Triangle =" +(t.getArea()));System.out.println("Perimeter of Triangle =" +(t.getPerimeter()));}}
19
Output ScreenOutput Screen
20
Extending InterfaceExtending Interface• One interface can inherit another interface using the
extends keyword and not the implements keyword. • For example,
interface A extends B { }
• Obviously, any class which implements a “sub-interface” will have to implement each of the methods contained in it’s “super-interface” also.
21
Abstract class and InterfaceAbstract class and Interface
Abstract class InterfaceA programmer uses an abstract class when there are some common features shared by all the objects.
A programmer writes an interface when all the features have different implementations for different objects.
Multiple inheritance not possible (Multiple “parent” interfaces)
Multiple inheritance possible (Only one “parent” class)
An abstract class contain both abstract and concrete(non abstract) method
An interface contain only abstract method
In abstract class, abstract keyword is compulsory to declare a method as an abstract
abstract keyword is optional to declare a method as an abstract in interface
An abstract class can have protected, public abstract method
An interface can have only public abstract method
Abstract class contain any type of variable
Interface contain only static final variable (constant)
22
23
Benefits of Interfaces Benefits of Interfaces
• Following concepts of object oriented programming can be achieved using Interface in JAVA.
1.Abstraction2.Multiple Inheritance3.polymorphism
Some of Java's Most used Some of Java's Most used InterfacesInterfaces
• IteratorTo run through a collection of objects without knowing how the
objects are stored, e.g., array.• CloneableUsed to make a copy of an existing object via the clone() method
on the class Object. This interface is empty.• SerializableUsed to Pack a group of objects such that it can be send over a
network or stored to disk. This interface is empty.• ComparableThe Comparable interface contains a compareTo method, and this method must take an Object parameter and return an integer
24
