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Interface :-

It is used to define set of rules which will be implemented by class,interface can contain complete description of particular component of an application.

for example if we develop Area class then how many area's will be calculated that will be decided by interface.



Syntax of Interface:-

interface  Intefacename
{


}


Rules for Interface:-

1) All methods of interface will be abstract and public by default.means interface only contain declaration of methods.


2) All methods of interface must be implemented into class.if we not implemented only single method then interface provide error


3) We should use implements keyword in interface to implement functionality in class .but in class we will use extends keyword.


Interface Area
{
    void rectangle();
    void circle();
}

class AreaImpl implements Area
{
     public void rectangle()
   {

   }
    public   void circle()
   {

   }

}



Advantage of Interface:-

1) Security :-  Interface provide data abstraction because we can declare functionality in interface and implemented by class then we can hide class from accessibility.


Interfacename ref = new Classname();

Area obj = new AreaImpl();

we should always create reference of interface to access class features then class reference will be hidden which is best for security.


2 Multiple Inheritance:-  We can combine common features of interfaces in a single class because interface has no functionality ,it has only declaration which not provide ambiguity problem.


3 Data contract:-  All method of interface must be implemented into class means interface provide data binding with implemented  class .



Example of interfaces with class:-

public interface Area {
    int a=200,b=12; //contsant
    void fun();
    void rect();
    void circle();
    void triangle();
   
}

public interface Ope {
    void fun();
    void add();
    void sub();
    
}


Interface Implementation:-

public class AreaImpl implements Area,Ope{

    
    public void rect() {
        System.out.println("area of rect is "+(a*b));
    }

    
    public void circle() {
        System.out.println("area of cirlce is "+(3.14F*a*a));
    }

    
    public void triangle() {
        System.out.println("area of triangle is "+(a*b)/2);
    }
    public static void main(String[] args) {
        Area obj = new AreaImpl();
        obj.circle();
        obj.rect();
        obj.triangle();
        obj.fun();
    }
    public void fun()
    {
        System.out.println("Function");
    }
    
    public void add() {
        System.out.println(a+b);
    }

   
    public void sub() {
        System.out.println(a-b);
    }
    
}


................................................................................

INTERFACE to INTERFACE EXAMPLE:-

We should use extends keyword to interface to interface always.

public interface A {
    void fun1();
}

public interface B extends A{
    void fun2();
}


public class c implements B{

    @Override
    public void fun2() {
        
    }

    @Override
    public void fun1() {
        
    }
    
}

.....................................................................................................................


Interface ,Class and Class

interface I
{
        void fun();
}
class C
{
     void fun1()
    {

     }
}
class D extends C implements I
{
        public void fun()
        {

        }

}

..................................................................

NOTE  class to interface never possible always interface will be parent and class will be child.






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