Java Interfaces and packages

 

               Interfaces and packages

 

Interfaces

Interfaces add most of the functionality that is required for many applications which would normally resort to using multiple inheritance in a language such as C++.

 

Defining an Interface

An interface is defined much like a class. This is the general from of an interface:

access interface name {

return-type method-name1(parameter-list);

return-type method-name2(parameter-list);

type final-varname1=value;

type final-varname2=value;

//...

return-type method-nameN(parameter-list);

type final-varnameN=value;

}

Implementing Interfaces

class->class = extends

class->interface = implement

//Program to illustrate interfaces

File name: Area.java

interface Area

{

        final static double pi=3.14;

        double compute(double x,double y);

}

File name: Rect1.java

class Rect1 implements Area

{

         public double compute(double x, double y)

       {

                  return(x*y);

       }

}

File name: Circle.java

class Circle implements Area

{

         public double compute(double x, double y)

       {

                  return(pi*x*x);

        }

}

File name: InterfaceTest.java

class InterfaceTest

{

         public static void main(String args[])

         {

         Rect1 r=new Rect1();

         Circle c=new Circle();

         Area area;

         area=r;

         System.out.println("Area of the Rectangle = "+area.compute(10,20));

         area=c;

           System.out.println("Area of the Rectangle = "+area.compute(10,0));

            }

}

Output

 

Packages

collection class, object,method

To run package use this command

javac –d . classname.java

//A simple package

File name: Add.java

package mypack;

public class Add

{

public void addition()

{

int a=100;

int b=200;

System.out.println("The sum is: "+(a+b));

}

}

File name: Myclass.java

import mypack.Add;

public class Myclass

{

public static void main(String args[])

{

Add a=new Add();

a.addition();

}

}

Output

Example

//Package Program : Save the following program in a directory called Math.

 

File Name : MathFun.java

package Math;

public class MathFun

{

public int fact(int num)

{

        if(num==1)

        return 1;

else

          return(num*fact(--num));

}

public int square(int num)

{

        return(num*num);

}

public int cube(int num)

{

      return(num*num*num);

}

public int sum(int a,int b)

{

         return(a+b);

}

public float sum(float a, float b)

{

         return(a+b);

}

 

public float multiply(float a, float b)

{

           return(a*b);

   }

}

Hint:- The following program to test the math package.Save the following program outside of math folder.

//File Name: PackTest.java

import Math.MathFun;

class PackTest

{

  public static void main(String args[])

 {

 MathFun mf=new MathFun();

System.out.println("Factorial:"+mf.fact(5));

System.out.println("Square:"+mf.square(5));

System.out.println("Cube:"+mf.cube(5));

System.out.println("Sum of Two Interger:"+mf.sum(5,5));

System.out.println("Sum of Two float Number:"+mf.sum(5.5f,5.3f));

    }

}

Output