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POWhy is the class CanvasPane not included in the Java API?
 

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  1. POWhy is the class CanvasPane not included in the Java API?
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    <p>** Why is the class CanvasPane not included in the Java API?.</p> <pre><code> import javax.swing.*; import java.awt.*; import java.awt.geom.*; /** * Class Canvas - a class to allow for simple graphical * drawing on a canvas. * * @author Michael Kolling (mik) * @author Bruce Quig * * @version 2008.03.30 */ public class Canvas { private JFrame frame; private CanvasPane canvas; private Graphics2D graphic; private Color backgroundColor; private Image canvasImage; /** * Create a Canvas with default height, width and background color * (300, 300, white) * @param title title to appear in Canvas Frame */ public Canvas(String title) { this(title, 300, 300, Color.white); } /** * Create a Canvas with default background color (white). * @param title title to appear in Canvas Frame * @param width the desired width for the canvas * @param height the desired height for the canvas */ public Canvas(String title, int width, int height) { this(title, width, height, Color.white); } /** * 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 color of the canvas */ public Canvas(String title, int width, int height, Color bgColor) { frame = new JFrame(); canvas = new CanvasPane(); frame.setContentPane(canvas); frame.setTitle(title); canvas.setPreferredSize(new Dimension(width, height)); backgroundColor = bgColor; frame.pack(); } /** * Set the canvas visibility and brings canvas to the front of screen * when made visible. This method can also be used to bring an already * visible canvas to the front of other windows. * @param visible boolean value representing the desired visibility of * the canvas (true or false) */ public void setVisible(boolean visible) { if(graphic == null) { // first time: instantiate the offscreen image and fill it with // the background color Dimension size = canvas.getSize(); canvasImage = canvas.createImage(size.width, size.height); graphic = (Graphics2D)canvasImage.getGraphics(); graphic.setColor(backgroundColor); graphic.fillRect(0, 0, size.width, size.height); graphic.setColor(Color.black); } frame.setVisible(true); } /** * Provide information on visibility of the Canvas. * @return true if canvas is visible, false otherwise */ public boolean isVisible() { return frame.isVisible(); } /** * Draw the outline of a given shape onto the canvas. * @param shape the shape object to be drawn on the canvas */ public void draw(Shape shape) { graphic.draw(shape); canvas.repaint(); } /** * Fill the internal dimensions of a given shape with the current * foreground color of the canvas. * @param shape the shape object to be filled */ public void fill(Shape shape) { graphic.fill(shape); canvas.repaint(); } /** * Fill the internal dimensions of the given circle with the current * foreground color of the canvas. */ public void fillCircle(int xPos, int yPos, int diameter) { Ellipse2D.Double circle = new Ellipse2D.Double(xPos, yPos, diameter, diameter); fill(circle); } /** * Fill the internal dimensions of the given rectangle with the current * foreground color of the canvas. This is a convenience method. A similar * effect can be achieved with the "fill" method. */ public void fillRectangle(int xPos, int yPos, int width, int height) { fill(new Rectangle(xPos, yPos, width, height)); } /** * Erase the whole canvas. */ public void erase() { Color original = graphic.getColor(); graphic.setColor(backgroundColor); Dimension size = canvas.getSize(); graphic.fill(new Rectangle(0, 0, size.width, size.height)); graphic.setColor(original); canvas.repaint(); } /** * Erase the internal dimensions of the given circle. This is a * convenience method. A similar effect can be achieved with * the "erase" method. */ public void eraseCircle(int xPos, int yPos, int diameter) { Ellipse2D.Double circle = new Ellipse2D.Double(xPos, yPos, diameter, diameter); erase(circle); } /** * Erase the internal dimensions of the given rectangle. This is a * convenience method. A similar effect can be achieved with * the "erase" method. */ public void eraseRectangle(int xPos, int yPos, int width, int height) { erase(new Rectangle(xPos, yPos, width, height)); } /** * Erase a given shape's interior on the screen. * @param shape the shape object to be erased */ public void erase(Shape shape) { Color original = graphic.getColor(); graphic.setColor(backgroundColor); graphic.fill(shape); // erase by filling background color graphic.setColor(original); canvas.repaint(); } /** * Erases a given shape's outline on the screen. * @param shape the shape object to be erased */ public void eraseOutline(Shape shape) { Color original = graphic.getColor(); graphic.setColor(backgroundColor); graphic.draw(shape); // erase by drawing background color graphic.setColor(original); canvas.repaint(); } /** * Draws an image onto the canvas. * @param image the Image object to be displayed * @param x x co-ordinate for Image placement * @param y y co-ordinate for Image placement * @return returns boolean value representing whether the image was * completely loaded */ public boolean drawImage(Image image, int x, int y) { boolean result = graphic.drawImage(image, x, y, null); canvas.repaint(); return result; } /** * Draws a String on the Canvas. * @param text the String to be displayed * @param x x co-ordinate for text placement * @param y y co-ordinate for text placement */ public void drawString(String text, int x, int y) { graphic.drawString(text, x, y); canvas.repaint(); } /** * Erases a String on the Canvas. * @param text the String to be displayed * @param x x co-ordinate for text placement * @param y y co-ordinate for text placement */ public void eraseString(String text, int x, int y) { Color original = graphic.getColor(); graphic.setColor(backgroundColor); graphic.drawString(text, x, y); graphic.setColor(original); canvas.repaint(); } /** * Draws a line on the Canvas. * @param x1 x co-ordinate of start of line * @param y1 y co-ordinate of start of line * @param x2 x co-ordinate of end of line * @param y2 y co-ordinate of end of line */ public void drawLine(int x1, int y1, int x2, int y2) { graphic.drawLine(x1, y1, x2, y2); canvas.repaint(); } /** * Sets the foreground color of the Canvas. * @param newColor the new color for the foreground of the Canvas */ public void setForegroundColor(Color newColor) { graphic.setColor(newColor); } /** * Returns the current color of the foreground. * @return the color of the foreground of the Canvas */ public Color getForegroundColor() { return graphic.getColor(); } /** * Sets the background color of the Canvas. * @param newColor the new color for the background of the Canvas */ public void setBackgroundColor(Color newColor) { backgroundColor = newColor; graphic.setBackground(newColor); } /** * Returns the current color of the background * @return the color of the background of the Canvas */ public Color getBackgroundColor() { return backgroundColor; } /** * changes the current Font used on the Canvas * @param newFont new font to be used for String output */ public void setFont(Font newFont) { graphic.setFont(newFont); } /** * Returns the current font of the canvas. * @return the font currently in use **/ public Font getFont() { return graphic.getFont(); } /** * Sets the size of the canvas. * @param width new width * @param height new height */ public void setSize(int width, int height) { canvas.setPreferredSize(new Dimension(width, height)); Image oldImage = canvasImage; canvasImage = canvas.createImage(width, height); graphic = (Graphics2D)canvasImage.getGraphics(); graphic.drawImage(oldImage, 0, 0, null); frame.pack(); } /** * Returns the size of the canvas. * @return The current dimension of the canvas */ public Dimension getSize() { return canvas.getSize(); } /** * Waits for a specified number of milliseconds before finishing. * This provides an easy way to specify a small delay which can be * used when producing animations. * @param milliseconds the number */ public void wait(int milliseconds) { try { Thread.sleep(milliseconds); } catch (InterruptedException e) { // ignoring exception at the moment } } /************************************************************************ * Inner class CanvasPane - the actual canvas component contained in the * Canvas frame. This is essentially a JPanel with added capability to * refresh the image drawn on it. */ private class CanvasPane extends JPanel { public void paint(Graphics g) { g.drawImage(canvasImage, 0, 0, null); } } } </code></pre>
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