Interface in java

Interface in Java
-Arulkumar V
Assistant Professor, SECE

Interface in Java
 An interface in java is a blueprint of a
class. It has static constants and abstract
methods.
 The interface in java is a mechanism to
achieve abstraction.
 There can be only abstract methods in the
java interface not method body. It is used to
achieve abstraction and multiple
inheritance in Java.
 Java Interface also represents IS-A
relationship.

Why use Java interface?
 There are mainly three reasons to
use interface. They are given below.
 It is used to achieve abstraction.
 By interface, we can support the
functionality of multiple inheritance.
 It can be used to achieve loose
coupling.

Example of Interface
interface printable{
void print();
}
class A6 implements printable{
public void print(){System.out.println("Hello");}
public static void main(String args[]){
A6 obj = new A6();
obj.print();
}
}
Printable interface has only one method, its
implementation is provided in the A class.

Example Program:
interface Drawable{
void draw();
}
//Implementation: by second user
class Rectangle implements Drawable{
public void draw(){System.out.println("drawi
ng rectangle");}
}
class Circle implements Drawable{
public void draw(){System.out.println("drawi
ng circle");} }

//Using interface: by third user
class TestInterface1{
Drawable d=new Circle();//In real scenario, obj
ect is provided by method e.g. getDrawable()
d.draw();
}}
Cont.,

Bank example
interface Bank{
float rateOfInterest();
}
class SBI implements Bank{
public float rateOfInterest(){return 9.15f;}
}
class PNB implements Bank{
public float rateOfInterest(){return 9.7f;}
}

Cont.,
class TestInterface2{
public static void main(String[] args){
Bank b=new SBI();
System.out.println("ROI: "+b.rateOfInter
est());
}}
Output:
ROI: 9.15

Multiple inheritance in Java by interface
If a class implements multiple interfaces, or an
interface extends multiple interfaces i.e. known as
multiple inheritance.

Multiple inheritance example
interface Printable{
void print();
}
interface Showable{
void show(); }
class A7 implements Printable,Showable
{
public void print(){System.out.println("Hello");
}
public void show()
{System.out.println("Welcome");}
public static void main(String args[])
{
A7 obj = new A7();
obj.print();
obj.show(); } }
Output: Hello
Welcome

Interface inheritance
A class implements interface but one interface extends another
interface .
interface Printable{
void print();
}
interface Showable extends Printable{
void show();
}
class TestInterface4 implements Showable{
public void print(){System.out.println("Hello");}
public void show(){System.out.println("Welcome");}
TestInterface4 obj = new TestInterface4();
obj.print();
obj.show();
}
} Hello
Welcome

Thank You
19-12-2017 Sampath Kumar.S, AP/IT 13

Interface in java

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