[2827] in java-interest
What does this error mean?
daemon@ATHENA.MIT.EDU (WAVELL RUFUS SEATON)
Mon Oct 16 23:43:34 1995
Date: Mon, 16 Oct 1995 19:48:03 -0600
From: WAVELL RUFUS SEATON <wavell@columbus.Colorado.EDU>
To: java-interest@java.sun.com
When I try and compile the following code I get this error:
CNDemo.java:71: Can't make a static reference to non static variable
canvas in class CNDemo.
canvas.getElem(i);
^
1 error
What does the error mean, and why can't I reference my canvas directly?
TIA, Bindu
P.S. Has anyone figured out how to create thick lines? I would like to draw
lines that are thicker than 1 pixel. I have two solutions, but they are slow,
one uses a filled pollygon, the other draws several lines... Neither are
very good or fast :(
------ SNIP ----------------------------------------------------------------
/*
* CNDraw.java 10/13/95 Bindu Wavell
*
* Implements a drawing package that is audio enabled for the ClassNotes+
* project.
*/
import java.applet.Applet;
import java.awt.*;
import java.util.Vector;
/*
* helper class that contains a segment of a drawing
*/
class Segment extends Object{
private int x1;
private int y1;
private int x2;
private int y2;
private int w;
private Color c;
Segment(int cx1, int cy1, int cx2, int cy2, int cw, Color cc) {
x1 = cx1; y1 = cy1; x2 = cx2; y2 = cy2; w = cw; c = cc;
}
public int getX1() { return x1; }
public int getY1() { return y1; }
public int getX2() { return x2; }
public int getY2() { return y2; }
public int getWidth() { return w; }
public Color getColor() { return c; }
}
/**
* An applet class that implements a Drawing interface with synchronized
* audio content for the ClassNotes+ Project at the Univerisy Of Colorado
* At Boulder.
*
* NOTE: drawing is an int since multiple mouse buttons can be pressed
* and so multiple mouse down events can occur before a mouse up
* event. This method will assume mouse down if any button is down
* so if button 1 is pressed, then button 2, then button 1 is
* released, the mouse is still considered down untill mouse 2
* is released.
*/
public class CNDraw extends Applet{
CNDrawCanvas canvas;
int x = 0;
int y = 0;
int drawing = 0;
/**
* Initialize CNDraw applet
*/
public void init() {
/* create simple layout for CNDraw */
setLayout(new BorderLayout());
/* create canvas for displaying demos */
canvas = new CNDrawCanvas();
/* create simple control bar */
Panel pBar = new Panel();
Panel pColors = new Panel();
Panel pSizes = new Panel();
/* add buttons to the color section */
pColors.add(new colorButton("Black", Color.black));
pColors.add(new colorButton("White", Color.white));
pColors.add(new colorButton("Red", Color.red));
pColors.add(new colorButton("Green", Color.green));
pColors.add(new colorButton("Blue", Color.blue));
pColors.add(new colorButton("Yellow", Color.yellow));
pColors.add(new colorButton("Gray", Color.lightGray));
pColors.add(new Button("Zoom"));
/* add radio buttons to size section */
CheckboxGroup cbg = new CheckboxGroup();
pSizes.add(new Label("Sizes: "));
pSizes.add(new Checkbox("1", cbg, true ));
pSizes.add(new Checkbox("2", cbg, false));
pSizes.add(new Checkbox("4", cbg, false));
pSizes.add(new Checkbox("8", cbg, false));
pSizes.add(new Checkbox("16", cbg, false));
pBar.setLayout(new GridLayout(2, 0));
pBar.add(pColors);
pBar.add(pSizes);
pColors.reshape(2,2,2,2);
pSizes.reshape(2,2,2,2);
/* create the final interface */
add("Center", canvas);
add("South", pBar);
} /* end init method */
/**
* main program startup code
*/
public static void main(String args[]) {
Frame fr = new Frame("CNDrawApplet");
CNDraw cnDemo = new CNDraw();
cnDemo.init();
cnDemo.start();
fr.add("Center", cnDemo);
fr.resize(300, 300);
fr.show();
} /* end main method */
/* main event handler for CNDraw */
public boolean handleEvent(Event e) {
if(e.target instanceof colorButton) {
canvas.setDefaultColor(((colorButton)e.target).getColor());
canvas.repaint();
} else if(e.target instanceof Checkbox) {
if(e.id == e.ACTION_EVENT) {
Checkbox cb = (Checkbox)(e.target);
canvas.setDefaultWidth(Integer.parseInt(cb.getLabel()));
}
} else if(e.target instanceof CNDrawCanvas) {
switch(e.id) {
case Event.MOUSE_DOWN:
drawing++;
/* only start a segment if this is the first mouse down */
if(drawing == 1) {
x = e.x;
y = e.y;
}
break;
case Event.MOUSE_DRAG:
if(drawing > 0) {
canvas.addSegment(new Segment(x, y, e.x, e.y, canvas.getWidth(),
canvas.getColor()));
x = e.x;
y = e.y;
canvas.repaint();
}
break;
case Event.MOUSE_UP:
drawing--;
break;
}
} else if (e.target instanceof Button) {
Button bt = (Button)(e.target);
if (bt.getLabel() == "Zoom") {
System.out.println("Got Zoom Click");
}
}
/* return super.handleEvent(e); */
return true;
}
} /* end CNDraw class */
class CNDrawCanvas extends Canvas {
String sMessage = "...Demo v0.2...";
Color cColor = Color.black;
int iWidth = 1;
Vector picture = new Vector();
public void paint(Graphics g) {
int w = size().width;
int h = size().height;
super.paint(g);
Segment sg;
int pn = picture.size();
/*
int xPoints[] = {0, 0, 0, 0};
int yPoints[] = {0, 0, 0, 0};
double slope;
double xOffset;
double yOffset;
*/
for (int i = 0; i < pn; i++) {
sg = (Segment)(picture.elementAt(i));
g.setColor(sg.getColor());
g.drawLine(sg.getX1(), sg.getY1(), sg.getX2(), sg.getY2());
}
/* Display message in the Center of the window */
g.setColor(cColor);
Font fn = g.getFont();
g.setFont(new Font(fn.getName(), fn.getStyle() + fn.BOLD,
fn.getSize() + 15));
FontMetrics fm = g.getFontMetrics();
int x = (w - fm.stringWidth(sMessage))/2;
int y = h/2;
g.drawString(sMessage, x , y);
} /* end paint method */
public void setMessage(String msg) { sMessage = msg; }
public void setDefaultColor(Color clr) { cColor = clr; }
public void setDefaultWidth(int width) { iWidth = width; }
public void addSegment(Segment sg) { picture.addElement(sg); }
public int getWidth() { return iWidth; }
public Color getColor() { return cColor; }
public Dimension minimumSize() { return new Dimension (20, 20); }
public Dimension preferedSize() { return new Dimension (300, 300); }
} /* end CNDrawCanvas class */
class colorButton extends Button {
Color cButton;
public colorButton(String lbl, Color clr) {
super(lbl);
cButton = clr;
setBackground(cButton);
/* !!! an attempt to hack buttons to have nice font color */
if ((clr == Color.blue) || (clr == Color.black)) {
setForeground(Color.white);
} else {
setForeground(Color.black);
}
}
public Color getColor() {
return cButton;
}
} /* end colorButton class */
------ SNIP ----------------------------------------------------------------
-
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