Question
Define an interface named Shape with a single method named area that calculates the area of the geometric shape:
public double area();
Next, define a class named Circle that implements Shape. The Circle class should have an instance variable for the radius, a constructor that sets the radius, accessor/mutator methods for the radius, and an implementation of the area method. Also define a class named Rectangle that implements Shape. The Rectangle class should have instance variables for the height and width, a constructor that sets the height and width, accessor and mutator methods for the height and width, and an implementation of the area method.
The following test code should then output the area of the Circle and Rectangle objects:
public static void main(String[] args)
{
Circle c = new Circle(4); // Radius of 4
Rectangle r = new Rectangle(4,3); // Height = 4, Width = 3
ShowArea(c);
ShowArea(r);
}
public static void ShowArea(Shape s)
{
double area = s.area();
System.out.println("The area of the shape is " + area);
}
Answer
//Shape interface
public interface Shape
{
//implements shape interface in class
public double area();
}
//Circle class definition
public class Circle implements Shape
{
//private member of class
private double radius;
//parameterized constructor
public Circle(double r)
{
radius = r;
}
//Returns the radius
public double getRadius()
{
return radius;
}
//Assign the new radius
public void setRadius(double newR)
{
radius = newR;
}
//Returns the area of the circle
public double area()
{
return radius * radius * Math.PI;
}
}
//The rectangle class implements the Shape interface
public class Rectangle implements Shape
{
//declare the private members
private double length;
private double width;
//constructor to set length and width
public Rectangle(double l, double w)
{
length = l;
width = w;
}
//Returns the length
public double getLength()
{
return length;
}
//Returns the width
public double getWidth()
{
return width;
}
//Assign the new value for length
public void setLength(double newL)
{
length = newL;
}
//Assign the new value for width
public void setWidth(double newW)
{
width = newW;
}
//returns the area of rectangle
public double area()
{
return length * width;
}
}
import java.io.*;
import java.util.*;
public class Drivertest
{
public static void main(String args[])
{
//create an object for circle class
Circle c = new Circle(4);
//create an object for rectangle class
Rectangle r = new Rectangle(4, 3);
//call the method ShowArea using Circle object
ShowArea(c);
//call the method ShowArea using rectangle object
ShowArea(r);
}
public static void ShowArea(Shape s)
{
double area = s.area();
System.out.println("The area of the shape is " + area);
}
}