GRAPHICAL USER INTERFACE :
CANVAS CLASS:
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: Bruce Quig
* @author: Michael Kšlling (mik)
*
* @version 2011.07.31
*/
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 Picture Demo", 500, 300,
Color.white);
}
canvasSingleton.setVisible(true);
return canvasSingleton;
}
// ----- instance part -----
private JFrame frame;
private CanvasPane canvas;
private Graphics2D graphic;
private Color backgroundColor;
private Image canvasImage;
private List<Object> objects;
private HashMap<Object, ShapeDescription> 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 bgColor the desired background color of the canvas
*/
private Canvas(String title, int width, int height, Color bgColor)
{
frame = new JFrame();
canvas = new CanvasPane();
frame.setContentPane(canvas);
frame.setTitle(title);
frame.setLocation(30, 30);
canvas.setPreferredSize(new Dimension(width, height));
backgroundColor = bgColor;
frame.pack();
objects = new ArrayList<Object>();
shapes = new HashMap<Object, ShapeDescription>();
}
/**
* 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(visible);
}
/**
* Draw a given shape onto the canvas.
* @param referenceObject an object to define identity for this shape
* @param color the color of the shape
* @param shape the shape object to be drawn on the canvas
*/
// Note: this is a slightly backwards way of maintaining the shape
// objects. It is carefully designed to keep the visible shape interfaces
// in this project clean and simple for educational purposes.
public void draw(Object referenceObject, String color, Shape shape)
{
objects.remove(referenceObject); // just in case it was already there
objects.add(referenceObject); // add at the end
shapes.put(referenceObject, new ShapeDescription(shape, color));
redraw();
}
/**
* Erase a given shape's from the screen.
* @param referenceObject the shape object to be erased
*/
public void erase(Object referenceObject)
{
objects.remove(referenceObject); // just in case it was already there
shapes.remove(referenceObject);
redraw();
}
/**
* Set the foreground color of the Canvas.
* @param newColor the new color for the foreground of the Canvas
*/
public void setForegroundColor(String colorString)
{
if(colorString.equals("red")) {
graphic.setColor(new Color(235, 25, 25));
}
else if(colorString.equals("black")) {
graphic.setColor(Color.black);
}
else if(colorString.equals("blue")) {
graphic.setColor(new Color(30, 75, 220));
}
else if(colorString.equals("yellow")) {
graphic.setColor(new Color(255, 230, 0));
}
else if(colorString.equals("green")) {
graphic.setColor(new Color(80, 160, 60));
}
else if(colorString.equals("magenta")) {
graphic.setColor(Color.magenta);
}
else if(colorString.equals("white")) {
graphic.setColor(Color.white);
}
else {
graphic.setColor(Color.black);
}
}
/**
* Wait 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 (Exception e)
{
// ignoring exception at the moment
}
}
/**
* Redraw ell shapes currently on the Canvas.
*/
private void redraw()
{
erase();
for(Object shape : objects) {
shapes.get(shape).draw(graphic);
}
canvas.repaint();
}
/**
* Erase the whole canvas. (Does not repaint.)
*/
private 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);
}
/************************************************************************
* 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);
}
}
/************************************************************************
* 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 ShapeDescription
{
private Shape shape;
private String colorString;
public ShapeDescription(Shape shape, String color)
{
this.shape = shape;
colorString = color;
}
public void draw(Graphics2D graphic)
{
setForegroundColor(colorString);
graphic.fill(shape);
}
}
}
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