I have written a server and client whiteboard program, and I keep getting "nullpointexceptions" after the program runs fine for a while - it appears almost random when the program fails, sometimes it happens to the server, sometimes it happens to a client(s).  I open the server first, then I run the clients.  the clients are duplicates,I just saved them under different names.

This is the Server: 

I have highlighted the line that gets the "nullpointerexception"

2. //EXC 19-4 SERVER white board with colors
3. 
   
4. //import net library
5. import processing.net.*;
6. 
   
7. //Declare a server and client object
8. Server server;
9. 
   
10. //tracks the number of clients connected
11. int clientCount = 0;
12. 
    
13. String incomingMessage = "";
14. 
    
15. PFont f;
16. 
    
17. void setup(){
18. 
    
19.   size(300, 200);
20.   background(255,0,0);
21. 
    
22.   //initialze server
23.   server = new Server(this, 5204);
24. 
    
25.   f = createFont("Chalkduster-48.vlw", 20, true);
26.   incomingMessage = "";
27. 
    
28. }//close setup
29. 
    
30. void draw(){
31. 
    
32.   background(255);
33.   Client client = server.available();
34. 
    
35.   if(client != null){
36. 
    
37.     incomingMessage = client.readStringUntil('*');
38.     server.write(incomingMessage);
39.     //println(incomingMessage);
40. 
    
41.   }//close if
42. 
    
43.   textFont(f);
44.   textAlign(CENTER);
45.   fill(0);
46.   text(incomingMessage, width/2, height/2 + 50);
47. 
    
48. 
    
49. }//close draw
50. 
    
51. void serverEvent(Server server, Client client){
52. 
    
53. 
    
54.   //incomingMessage = "A new client has connected" + client.ip();
55.   println("A new client has connected at IP: " + client.ip());
56. 
    
57.   //server.write(clientCount);
58.   clientCount += 1;
59. 
    
60. }//close serverEvent

This is the client...

I have highlighted the line that gets the "nullpointerexception"

2. //EXC 19-4 client white board with colors
3. import processing.net.*;
4. 
   
5. Client client;
6. 
   
7. color r;
8. color g;
9. color b;
10. 
    
11. color lineColor;
12. 
    
13. void setup(){
14. 
    
15.   lineColor = color(0);
16.   frame.setTitle("My super-awesome application!!!");
17.   size(200, 200);
18.   background(255);
19. 
    
20.   client = new Client(this, "127.0.0.1", 5204);
21. 
    
22.   r = color(255,0,0);
23.   g = color(0,255,0);
24.   b = color(0,0,255);
25. 
    
26. }//close setup
27. 
    
28. void draw(){
29. 
    
30.   if(client.available() > 10){
31. 
    
32.     String recieve = client.readStringUntil('*');
33.     println("receiving data = " + recieve);
34.     int[] values = int( splitTokens( recieve, ",*" ) );
35. 
    
36.     //render ellipses
37.     noStroke();
38.     fill(values[2]);
39.     ellipse(values[0], values[1], 10, 10);
40. 
    
41.   }//close if
42. }//
43. 
    
44. void mouseDragged(){
45. 
    
46.   String send = mouseX + "," + mouseY + "," + lineColor + "*";
47.   client.write(send);
48.   println("sending data = " + send);
49. 
    
50. }//close if
51. 
    
52. void keyPressed(){
53. 
    
54.   if(key == 'c'){
55. 
    
56.     background(255);
57. 
    
58.   }
59.   else if(key == 'r'){
60. 
    
61.     lineColor = r;
62. 
    
63.   } else if(key == 'g'){
64. 
    
65.     lineColor = g;
66. 
    
67.   }  else if(key == 'b'){
68. 
    
69.     lineColor = b;
70. 
    
71.   }//close if
72. }//close mousepressed