Question

Shapes2D

Write the following four classes to practice using an abstract class and polymorphism. Submit all four classes.

Shape2D class

For this class, include just an abstract method name get2DArea() that returns a double.

Rectangle2D class

Make this class inherit from the Shape2D class. Have it store a length and a width as fields. Provide a constructor that takes two double arguments and uses them to set the fields. Note, the area of a rectangle is the length times the width.

Circle2D class

Also make this class inherit from the Shape2D class. Have it store a radius as a field. Provide a constructor that takes a double argument and uses it to set the field. Note, the area of a circle is PI times it's radius times it's radius.

Shape2DDriver class

Have this class provide a method named displayName() that takes an object from just any of the above three classes (you can't use an Object type parameter). Have the method display the area of the object, rounded to one decimal place.

Answer 1

The following points can be followed to create the mentioned four classes:

• The abstract keyword will be used for making the class Shape2D as abstract. The get2DArea() method will be kept empty.
• Classes Rectangle2D and Circle2D will be created. These classes will extend the Shape2D abstract class.
• Define the constructor and get2DArea() for each subclass based on the data members.
• Define a method displayName() in a class Shape2DDriver.
• In this class, create objects from the subclasses.
• The method displayName() will display the area of the passed object.

The java program:

import java.lang.Math.*;
import java.text.DecimalFormat;
//abstract class Shape2D
abstract class Shape2D{
    abstract double get2DArea();
}
//class Retangle2D
class Retangle2D extends Shape2D{
    
    //data members
    private double length;
    private double width;
    
    //constructor
    Retangle2D(double l,double w){
        length = l;
        width = w;
    }
    
    //method to get area
    public double get2DArea(){
        return length * width;
    }
}
//class Circle2D
class Circle2D extends Shape2D{
    
    //date member
    private double radius;
    
    //constructor
    Circle2D(double r){
        radius = r;
    }
    
    //method to get area
    public double get2DArea(){
        return Math.PI * radius * radius;
    }
}
public class Shape2DDriver
{
 public static void main(String[] args) {
 
 //Object of Circle2D
 Circle2D c = new Circle2D(6);
 
 //Object of Retangle2D
 Retangle2D r = new Retangle2D(11,8);
 
 //area of Circle
 displayName(c);
 
 //area of Retangle
 displayName(r);
 
 //using abstract class
 Shape2D s = new Retangle2D(7,5);
 
 displayName(s);
 
 }
 
 //method displayName
 static void displayName(Shape2D obj){
     
     //format to round upto one decimal
     DecimalFormat df = new DecimalFormat("#.#");
        
        //print the Area of the object
     System.out.println("Area :" + df.format(obj.get2DArea()) );
 }
}

Sample output: