[4371] in java-interest
NullPointerException from drawLine() inside a thread in paint() ??
daemon@ATHENA.MIT.EDU (Eric Ho)
Thu Dec 21 01:37:54 1995
Date: Thu, 21 Dec 95 00:04:15 EST
From: eric@internet.sbi.com (Eric Ho)
To: java-interest-digest@java.sun.com
Greetings Everyone,
I'm not sure if this is a bug or not in the appletviewer (JDK b1).
I've a canvas and in its overriden paint() method, I tried to do some simple
drawings in a separate thread. Calling Graphics' setColor() is fine but
calling drawLine() greeted me with a NullPointerException.
Am I missing something ??
Any pointers/info much appreciated.
Here is the sample code :-
------------8<------- CUT HERE -----------8<-----------
import java.applet.*;
import java.lang.*;
public class Simple extends java.applet.Applet {
public void init() {
setLayout(new BorderLayout());
add("Center", new MyCanvas());
}
public static void main(String args[]) {
Frame f = new Frame("Simple");
Simple t = new Simple();
t.init();
t.start();
f.add("Center", t);
f.resize(400, 400);
f.show();
}
}
class MyCanvas extends java.awt.Canvas {
public void paint(Graphics g) {
CreativeBrush cb = new CreativeBrush(g);
new Thread(cb).start();
System.out.println("MyCanvas.paint(): Done."); System.out.flush();
}
}
class CreativeBrush implements Runnable {
Graphics gcontext;
public CreativeBrush(Graphics g) {
this.gcontext = g;
}
public void run() {
System.out.println("run(): starts."); System.out.flush();
CrazyDrawings();
System.out.println("run(): done."); System.out.flush();
}
void CrazyDrawings() {
gcontext.setColor(Color.orange);
System.out.println("CrazyDrawings(): starts."); System.out.flush();
gcontext.drawLine(10, 10, 90, 90); // <<=== *** PROBLEM HERE *****
System.out.println("CrazyDrawings(): Done."); System.out.flush();
}
}
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-Eric Ho- eric@sbi.com
-
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