Answer:
Java program is explained below
Explanation:
Implemented the Circle and Square subclasses. And modified the PolyDemo class to use them. Use the following files along with Shape and Spray classes.
To indent code in eclipse, select code and press Ctrl+a and then Ctrl+i.
Please don't forget to rate the answer if it helped. Post a comment in case of any issues.
PolyDemo.java( modified)
import java.util.*;
import javax.swing.*;
import java.awt.*;
/*
* Class PolyDemo (is a JFrame) and PolyDemoPanel (is a JPanel)
*
* Author: Rob Nash
*/
class PolyDemo extends JFrame {
public PolyDemo() {
getContentPane().add( new PolyDemoPanel() );
//just some windowing stuff that must happen for all Frames
setSize( 300,300 );
setVisible( true );
setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
}
public static void main( String args[] ) {
PolyDemo myApp = new PolyDemo();
}
//this is our first "inner" or internal class
//the purpose of this class is solely to support the JFrame class above, and I don't want it reused in arbitrary contexts, so by nesting this class here
//I can indicate the intent a bit more clearly that this class "goes with" the class above it
//In general, each class is a separate entity that should be contained in a separate file
public class PolyDemoPanel extends JPanel {
Shape[] myShapes= new Shape[20];
public PolyDemoPanel() {
//Shape a = new Shape( getRandInt(), getRandInt());
//Shape b = new Circle( getRandInt(), getRandInt(), getRandInt() );
//a = new Square(getRandInt(), getRandInt(), getRandInt(), getRandInt() );
//a = getRandShape();
//( (Circle) b ).getRadius();
/*********************************************************************************************************************
* Code for populating our myShapes changes minimally when new classes are introduced (only in getRandShape())
*********************************************************************************************************************/
for( int i = 0; i < 20; i++ ) {
myShapes[i] = getRandShape();
}
}
/*********************************************************************************************************************
* Code for drawing our shapes doesn't change at all! Since we intended to take advantage of polymorphism, we coded
* this "in general" with respect to the superclass, and not specific to any subclass.
*********************************************************************************************************************/
public void paint( Graphics g ) {
super.paint(g); //don't remove - required for GUI widgets to draw correctly
/************************
* Late Binding Demo
************************/
for( int i = 0; i < myShapes.length; i++ ){
//which draw method is invoked here? There are many forms of the method (polymorphic), so which is chosen?
//Java has RTTI about every object, and it uses this info to choose the correct method to invoke!
myShapes[i].draw( g );
}
}
public int getRandInt() {
return ( (int) ( Math.random() * 200 ) );
}
public Shape getRandShape() {
Shape retVal = null;
final int x = getRandInt();
final int y = getRandInt();
/********************************
* Polymorphic extensibility demo
*
*******************************/
switch( ( int )(Math.random() * 4) ) {
case 0: retVal = new Square( x, y, getRandInt(), getRandInt());
break;
case 1: retVal = new Spray( x,y );//Cube( x, y, getRandInt(), getRandInt(), getRandInt() );
break;
case 2: retVal = new Spray( x,y );
break;
case 3: retVal = new Circle( x,y,getRandInt() );////new Cylinder( x,y, getRandInt(), getRandInt() );
break;
}
return retVal;
}
}
}
Circle.java
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
public class Circle extends Shape {
private int radius;
public Circle(int x, int y, int radius)
{
super(x,y);
this.radius = radius;
}
double getRadius()
{
return radius;
}
void setRadius(int rad)
{
this.radius = rad;
}
@Override
public double getArea() {
return Math.PI * radius * radius;
}
@Override
public void draw(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
g.setColor(Color.red);
g2d.drawOval(getX(), getY(), radius, radius);
}
}
Square.java
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
public class Square extends Shape {
private int width;
private int height;
public Square(int x, int y, int width, int height) {
super(x,y);
this.width = width;
this.height = height;
}
public int getWidth() {
return width;
}
public void setWidth(int width) {
this.width = width;
}
public int getHeight() {
return height;
}
public void setHeight(int height) {
this.height = height;
}
@Override
public double getArea() {
return width * height;
}
@Override
public void draw(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
g.setColor(Color.blue);
g2d.drawRect(getX(), getY(), width, height);
}
}
