为什么Java API中不包含CanvasPane类? [英] Why is the class CanvasPane not included in the Java API?
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问题描述
**为什么Java API中不包含CanvasPane类?
** Why is the class CanvasPane not included in the Java API?.
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);
}
}
}
推荐答案
为什么应该这样?我的意思是说它是BlueJ扩展类AFAIK.关于StringUtils或NumberUtils，可能会想到类似的问题.恕我直言，这两个确实符合原始Java API的要求. :)
Why it should be? I mean its a BlueJ extension class, AFAIK. Similar questions may come to the mind regarding StringUtils, or NumberUtils. IMHO, these two really qualifies to be there in the original Java API. :)
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