Implementing Interfaces in Java…
Example : Program to illustrate interfaces
import java.io.*;
interface Area
{
final static double pi=3.14;
double compute(double x,double y);
}
class Rect implements Area
{
public double compute(double x,double y)
{
return(x*y);
}
}
class Circle implements Area
{
public double compute(double x,double y)
{
return(pi*x*x);
}
}
class InterfaceTest
{
public static void main(String args[])
{
Rect r=new Rect();
Circle c=new Circle();
Area area;
area=r;
System.out.println("Area of Rectangle="+area.compute(10,20));
area=c;
System.out.println("Area of Circle="+area.compute(10,0));
}
}
import java.io.*;
interface Area
{
final static double pi=3.14;
double compute(double x,double y);
}
class Rect implements Area
{
public double compute(double x,double y)
{
return(x*y);
}
}
class Circle implements Area
{
public double compute(double x,double y)
{
return(pi*x*x);
}
}
class InterfaceTest
{
public static void main(String args[])
{
Rect r=new Rect();
Circle c=new Circle();
Area area;
area=r;
System.out.println("Area of Rectangle="+area.compute(10,20));
area=c;
System.out.println("Area of Circle="+area.compute(10,0));
}
}
import java.io.*; interface Area { final static double pi=3.14; double compute(double x,double y); } class Rect implements Area { public double compute(double x,double y) { return(x*y); } } class Circle implements Area { public double compute(double x,double y) { return(pi*x*x); } } class InterfaceTest { public static void main(String args[]) { Rect r=new Rect(); Circle c=new Circle(); Area area; area=r; System.out.println("Area of Rectangle="+area.compute(10,20)); area=c; System.out.println("Area of Circle="+area.compute(10,0)); } }

Classpath in Java…
Example : A simple package
import java.io.*;
class Balance
{
String name;
double bal;
Balance(String n,double b)
{
name=n;
bal=b;
}
void show()
{
if(bal<0)
System.out.println("-->");
System.out.println(name+":$"+bal);
}
}
class AccountBalance
{
public static void main(String args[])
{
Balance current[]=new Balance[3];
current[0]=new Balance("K.J.Fielding",123.123);
current[1]=new Balance("Will Tell",145.33);
current[2]=new Balance("Tom Jackson",-32.3);
for(int i=0;i<3;i++)current[i].show();
}
}
import java.io.*;
class Balance
{
String name;
double bal;
Balance(String n,double b)
{
name=n;
bal=b;
}
void show()
{
if(bal<0)
System.out.println("-->");
System.out.println(name+":$"+bal);
}
}
class AccountBalance
{
public static void main(String args[])
{
Balance current[]=new Balance[3];
current[0]=new Balance("K.J.Fielding",123.123);
current[1]=new Balance("Will Tell",145.33);
current[2]=new Balance("Tom Jackson",-32.3);
for(int i=0;i<3;i++)current[i].show();
}
}
import java.io.*; class Balance { String name; double bal; Balance(String n,double b) { name=n; bal=b; } void show() { if(bal<0) System.out.println("-->"); System.out.println(name+":$"+bal); } } class AccountBalance { public static void main(String args[]) { Balance current[]=new Balance[3]; current[0]=new Balance("K.J.Fielding",123.123); current[1]=new Balance("Will Tell",145.33); current[2]=new Balance("Tom Jackson",-32.3); for(int i=0;i<3;i++)current[i].show(); } }

Importing Packages in Java…
Package program : Save the following program in a directory called Math.
FileName : MathFun.java
//import java.io.*;
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 int multiply(int a,int b)
{
return(a*b);
}
public float multiply(float a,float b)
{
return(a*b);
}
}
//import java.io.*;
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 int multiply(int a,int b)
{
return(a*b);
}
public float multiply(float a,float b)
{
return(a*b);
}
}
//import java.io.*; 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 int multiply(int a,int b) { return(a*b); } public float multiply(float a,float b) { return(a*b); } }
Hint : Save the following program outside of Math folder.
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 Integers:"+mf.sum(5,5));
System.out.println("Sum of Two Float Numbers:"+mf.sum(5.5f,5.3f));
}
}
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 Integers:"+mf.sum(5,5));
System.out.println("Sum of Two Float Numbers:"+mf.sum(5.5f,5.3f));
}
}
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 Integers:"+mf.sum(5,5)); System.out.println("Sum of Two Float Numbers:"+mf.sum(5.5f,5.3f)); } }
