* Standard drawing library. This class provides a basic capability for
* creating drawings with your programs. It uses a simple graphics model that
* allows you to create drawings consisting of points, lines, and curves
* in a window on your computer and to save the drawings to a file.
*
* Todo
* ----
* - Add support for gradient fill, etc.
*
* Remarks
* -------
* - don't use AffineTransform for rescaling since it inverts
* images and strings
* - careful using setFont in inner loop within an animation -
* it can cause flicker
*
*************************************************************************/

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.awt.image.*;
import java.io.*;
import java.net.*;
import java.util.LinkedList;
import java.util.TreeSet;
import javax.imageio.ImageIO;
import javax.swing.*;

/**
* Standard draw. This class provides a basic capability for
* creating drawings with your programs. It uses a simple graphics model that
* allows you to create drawings consisting of points, lines, and curves
* in a window on your computer and to save the drawings to a file.
* 
* For additional documentation, see <a href="http://introcs.cs.princeton.edu/15inout">Section 1.5</a> of
* Introduction to Programming in Java: An Interdisciplinary Approach by Robert Sedgewick and Kevin Wayne.
*
* @author
* @author
*/
public final class StdDraw implements ActionListener, MouseListener, MouseMotionListener, KeyListener {

// pre-defined colors
public static final Color BLACK = Color.BLACK;
public static final Color BLUE = Color.BLUE;
public static final Color CYAN = Color.CYAN;
public static final Color DARK_GRAY = Color.DARK_GRAY;
public static final Color GRAY = Color.GRAY;
public static final Color GREEN = Color.GREEN;
public static final Color LIGHT_GRAY = Color.LIGHT_GRAY;
public static final Color MAGENTA = Color.MAGENTA;
public static final Color ORANGE = Color.ORANGE;
public static final Color PINK = Color.PINK;
public static final Color RED = Color.RED;
public static final Color WHITE = Color.WHITE;
public static final Color YELLOW = Color.YELLOW;

/**
* Shade of blue used in Introduction to Programming in Java.
* It is Pantone 300U. The RGB values are approximately (9, 90, 166).
*/

public static final Color BOOK_BLUE = new Color( 9, 90, 166);
public static final Color BOOK_LIGHT_BLUE = new Color(103, 198, 243);

/**
* Shade of red used in Algorithms 4th edition.
* It is Pantone 1805U. The RGB values are approximately (150, 35, 31).
*/

public static final Color BOOK_RED = new Color(150, 35, 31);

// default colors
private static final Color DEFAULT_PEN_COLOR = BLACK;
private static final Color DEFAULT_CLEAR_COLOR = WHITE;

// current pen color
private static Color penColor;

// default canvas size is DEFAULT_SIZE-by-DEFAULT_SIZE
private static final int DEFAULT_SIZE = 512;
private static int width = DEFAULT_SIZE;
private static int height = DEFAULT_SIZE;

// default pen radius
private static final double DEFAULT_PEN_RADIUS = 0.002;

// current pen radius
private static double penRadius;

// show we draw immediately or wait until next show?
private static boolean defer = false;

// boundary of drawing canvas, 5% border
private static final double BORDER = 0.05;
private static final double DEFAULT_XMIN = 0.0;
private static final double DEFAULT_XMAX = 1.0;
private static final double DEFAULT_YMIN = 0.0;
private static final double DEFAULT_YMAX = 1.0;
private static double xmin, ymin, xmax, ymax;

// for synchronization
private static Object mouseLock = new Object();
private static Object keyLock = new Object();

// default font
private static final Font DEFAULT_FONT = new Font("SansSerif", Font.PLAIN, 16);

// current font
private static Font font;

// double buffered graphics
private static BufferedImage offscreenImage, onscreenImage;
private static Graphics2D offscreen, onscreen;

// singleton for callbacks: avoids generation of extra .class files
private static StdDraw std = new StdDraw();

// the frame for drawing to the screen
private static JFrame frame;

// mouse state
private static boolean mousePressed = false;
private static double mouseX = 0;
private static double mouseY = 0;

// queue of typed key characters

private static LinkedList<Character> keysTyped = new LinkedList<Character>();

// set of key codes currently pressed down

private static TreeSet<Integer> keysDown = new TreeSet<Integer>();

// singleton pattern: client can't instantiate

private StdDraw() { }

// static initializer

static { init(); }

/**
* Set the window size to the default size 512-by-512 pixels.
*/

public static void setCanvasSize() {
 setCanvasSize(DEFAULT_SIZE, DEFAULT_SIZE);
}

/**
* Set the window size to w-by-h pixels.
*
* @param w the width as a number of pixels
* @param h the height as a number of pixels
* @throws IllegalArgumentException if the width or height is 0 or negative
*/

public static void setCanvasSize(int w, int h) {
 if (w < 1 || h < 1) throw new IllegalArgumentException("width and height must be positive");
 width = w;
 height = h;
 init();
}

// init
private static void init() {
 if (frame != null) frame.setVisible(false);
 frame = new JFrame();
 offscreenImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
 onscreenImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
 offscreen = offscreenImage.createGraphics();
 onscreen = onscreenImage.createGraphics();
 setXscale();
 setYscale();
 offscreen.setColor(DEFAULT_CLEAR_COLOR);
 offscreen.fillRect(0, 0, width, height);
 setPenColor();
 setPenRadius();
 setFont();
 clear();

 // add antialiasing
 RenderingHints hints = new RenderingHints(RenderingHints.KEY_ANTIALIASING,
 RenderingHints.VALUE_ANTIALIAS_ON);
 hints.put(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
 offscreen.addRenderingHints(hints);

 // frame stuff
 ImageIcon icon = new ImageIcon(onscreenImage);
 JLabel draw = new JLabel(icon);

 draw.addMouseListener(std);
 draw.addMouseMotionListener(std);

 frame.setContentPane(draw);
 frame.addKeyListener(std); // JLabel cannot get keyboard focus
 frame.setResizable(false);
 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // closes all windows
 // frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); // closes only current window
 frame.setTitle("Standard Draw");
 frame.setJMenuBar(createMenuBar());
 frame.pack();
 frame.requestFocusInWindow();
 frame.setVisible(true);
}

// create the menu bar (changed to private)

private static JMenuBar createMenuBar() {
 JMenuBar menuBar = new JMenuBar();
 JMenu menu = new JMenu("File");
 menuBar.add(menu);
 JMenuItem menuItem1 = new JMenuItem(" Save... ");
 menuItem1.addActionListener(std);
 menuItem1.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_S,
 Toolkit.getDefaultToolkit().getMenuShortcutKeyMask()));
 menu.add(menuItem1);
 return menuBar;
}

/*************************************************************************
* User and screen coordinate systems
*************************************************************************/

/**
* Set the x-scale to be the default (between 0.0 and 1.0).
*/

public static void setXscale

With this program you are going to design a math practice program f...