I modified someone's clock sketch (sorry, the source doesn't mention authorship and I forgot where I found it) to be a class (one of the recommended ways to learn about classes is to covert sketches to classes).  I've noticed that maybe 30% of the time I launch my app containing this class, that I get a ClassNotFoundException with this or one of several other classes used in the sketch. 

So first, as a general issue, what can cause a sketch to generate class not found exceptions on an intermittent basis -- sometimes the sketch runs fine and other times it acts as if a class were not defined or present in the sketch?

Second, what do the numbers at the end of each line in a debug window mean?  I thought they were line numbers, but, if they are, they are useless in the processing.org editor if a sketch has multiple separate files organized as tabs because the line numbers count all the lines in the sketch sequentially, but, when looking at a sketch in the processing editor, the code in each tab begins with 1. 

Here's what I get when it can't find a class:

processing.app.debug.RunnerException: ClassNotFoundException: Feed_Reader$Clock
    at processing.app.Sketch.placeException(Sketch.java:1543)
    at processing.app.debug.Runner.findException(Runner.java:582)
    at processing.app.debug.Runner.reportException(Runner.java:558)
    at processing.app.debug.Runner.exception(Runner.java:498)
    at processing.app.debug.EventThread.exceptionEvent(EventThread.java:367)
    at processing.app.debug.EventThread.handleEvent(EventThread.java:255)
    at processing.app.debug.EventThread.run(EventThread.java:89)
processing.app.debug.RunnerException: ClassNotFoundException: Feed_Reader$Clock
    at processing.app.Sketch.placeException(Sketch.java:1543)
    at processing.app.debug.Runner.findException(Runner.java:582)
    at processing.app.debug.Runner.reportException(Runner.java:558)
    at processing.app.debug.Runner.exception(Runner.java:498)
    at processing.app.debug.EventThread.exceptionEvent(EventThread.java:367)
    at processing.app.debug.EventThread.handleEvent(EventThread.java:255)
    at processing.app.debug.EventThread.run(EventThread.java:89)
Exception in thread "Animation Thread" java.lang.NoClassDefFoundError: Feed_Reader$Clock
    at Feed_Reader.setup(Feed_Reader.java:111)
    at processing.core.PApplet.handleDraw(Unknown Source)
    at processing.core.PApplet.run(Unknown Source)
    at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.ClassNotFoundException: Feed_Reader$Clock
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
    ... 4 more

Here's the block of code in my main sketch's setup() where I call some of the separate classes used in the sketch; note myClock on line 3:

1.   myMoonImage = new MoonImage(width-((width/4))+60,(height/2),#3FB748,255);
2.   myRadarImage = new RadarImage(260,50,#3FB748,255);
3.   myClock = new Clock(width-((width/4))+60,(height/2),105);
4.   myTrafficCams = new TrafficCams(width-((width/2))+45,(height/2)+13,172,128,255,255,4);
5.  
6.   myWeather = new Weather(260,65,#3FB748);
7.   myWaves = new Waves(4,100,#3FB748);
8.   myTides = new Tides(12,134,#3FB748,60);

Sometimes the classnotfoundexception occurs for one of the other classes and I don't think it's caused by a bug in a particular class, but, for example, here's the myClock class being called:

1. public class Clock {
2.   float  d, mm, wCen, hCen, Cir, CirR1, CirR2, CirR3;
3.   String f;
4.   PFont b;
5.  
6.  
7.  Clock(int _wCen, int _hCen, int _Cir){
8.    wCen = _wCen;
9.    hCen = _hCen;
10.    Cir = _Cir;
11.    b = loadFont ("Andalus-48.vlw");
12.    }
13.   
14.  public void display() {
15.  smooth();
16.  stroke(255);
17.  fill(130);
18.  textFont(b,32);  
19.  int d = day();  
20.  int mm = month();
21.  int yy = year()-2000;
22.  String f =  nf(mm,2) + "." + nf(d,2) + "." + str(yy); //nf(yy,4);
23.  text(f,wCen-55, hCen+65);  
24.  
25.  // time
26.  
27. //   wCen = width-((width/4)+50);
28. //   hCen = height/2;
29.    //Cir = 150;
30.    CirR1 = Cir/3;
31.    CirR2 = Cir/2.5;
32.    CirR3 = Cir/4; 
33.  
34.   fill(200);  
35.   float s = map(second(), 0, 60, 0, TWO_PI) - HALF_PI;
36.   float m = map(minute(), 0, 60, 0, TWO_PI) - HALF_PI;
37.   float h = map(hour()% 12, 0, 12,0, TWO_PI) - HALF_PI;
38.   stroke(194); 
39.   ellipse(wCen, hCen, 6, 6);
40.   strokeWeight(1);
41.   line(wCen, hCen, cos(s) * CirR1 + wCen, sin(s) * CirR1 + hCen);
42.   strokeWeight(2);
43.   line(wCen, hCen, cos(m) * CirR2 + wCen, sin(m) * CirR1 + hCen);
44.   strokeWeight(3.5);
45.   line(wCen, hCen, cos(h) * CirR3 + wCen, sin(h) * CirR1 + hCen);
46.  }
47. }

Not knowing any better, I've thought about putting delay(1000) in between calling each class in case it was a problem with loading too many classes too quickly.  In case you're wondering, it's a localized news aggregator with visualizations for wave height, sunset, moonrise ... still very much underdevelopment.