Java Programming - Polka Dots Code

The PolkaDots project makes use of the Canvas class and the Circle class from the Shapes project.
Write the PolkaDots code.

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import javax.swing.*;
import java.awt.*;
import java.util.List;
import java.util.*;

/**
* Canvas is a class to allow for simple graphical drawing on a canvas. This is
* a modification of the general purpose Canvas, specially made for the BlueJ
* "shapes" example.
*
* @author:
* @author:
*
* @version: 1.6 (shapes)
*/
public class Canvas {

   
    // Note: The implementation of this class (specifically the handling of
    // shape identity and colors) is slightly more complex than necessary. This
    // is done on purpose to keep the interface and instance fields of the
    // shape objects in this project clean and simple for educational purposes.

    private static Canvas canvasSingleton;

    /**
    * Factory method to get the canvas singleton object.
    */
    public static Canvas getCanvas() {
       if (canvasSingleton == null) {
            canvasSingleton = new Canvas("BlueJ Shapes Demo", 300, 300,
                   Color.white);
       }
       canvasSingleton.setVisible(true);
       return canvasSingleton;
    }

    // ----- instance part -----
    private JFrame frame;
    private CanvasPane canvas;
    private Graphics2D graphic;
    private Color backgroundColour;
    private Image canvasImage;
    private List objects;
    private HashMap shapes;

    /**
    * Create a Canvas.
    *
    * @param title title to appear in Canvas Frame
    * @param width the desired width for the canvas
    * @param height the desired height for the canvas
    * @param bgClour the desired background colour of the canvas
    */
    private Canvas(String title, int width, int height, Color bgColour) {
       frame = new JFrame();
       canvas = new CanvasPane();
       frame.setContentPane(canvas);
       frame.setTitle(title);
       canvas.setPreferredSize(new Dimension(width, height));
       backgroundColour...