I am trying to use noFill() to "color" a rect "clear", that is, I want the rect to be "see through", so the images I have behind it can be seen.  In my program, I have a bunch of colored rectangles in cols and rows that cover the whole display window, and as the mouse moves across the screen, a loop is comparing an array of mouse positions to the position of the rectangles covering the screen, if a match is made, the rect is noFill() - i can see through the rect - if a match is not made, the rect is filled with a solid color.  I have 20 mouse position that increment with each new mouse input to make a  trail effect.  But it doesn't work right, when I use noFill() only 1 rect in my array ends up actually "see through", but when i specify a color with fill(), it works just fine.  I have also messed with using fill() with an alpha value of "0", and this doesn't work quite right either...any help would be great!

2. //EXC 19_5
3. 
   
4. //this is the size of each sheild unit, the smaller, the more difficult to uncover
5. int sheild = 20;
6. 
   
7. //this is the length of the uncover array, the bigger the number the easier to uncover the sheild
8. int strength = 20;
9. 
   
10. //this stops the sheild loop when a matching mouseX/Y position in the uncover array is detected
11. int matches = 0;
12. 
    
13. //this is the uncover array, it stores the last x mouse positions, and removes the sheild from those points
14. int[] uncoverX = new int[strength];
15. int[] uncoverY = new int[strength];
16. 
    
17. //this increments the uncover array
18. int inc = 0;
19. 
    
20. Token[] square = new Token[4];
21. 
    
22. int score = 0;
23. 
    
24. void setup(){
25. 
    
26.   size(600,400);
27.   smooth();
28.   background(255);
29.   
30.   for(int i = 0; i < 4; i++){
31. 
    
32.     square[i] = new Token();
33. 
    
34.   }//close for loop
35. 
    
36. }//close setup
37. 
    
38. void draw(){
39. 
    
40.   background(255);
41. 
    
42.   for(int i = 0; i < 4; i++){
43. 
    
44.     square[i].display();
45. 
    
46.   }//close for loop
47. 
    
48. 
    
49.   //cover the board with the sheild
50.   for(int i = 0; i < width; i = i+sheild){
51. 
    
52.     for(int j = 0; j < height; j = j+sheild){
53.     
54.       matches = 0;
55.    
56.       //check where  sheild and uncover array overlap
57.       for(int q = 0; q < strength; q++){
58.         
59.          
60.           if( (uncoverX[q] >= i && uncoverX[q] <= i + sheild) && (uncoverY[q] >= j && uncoverY[q] <= j + sheild) ){
61.           
62.           
63.         //fill(255); //This works like I expect noFill() should work...
64.         noFill();
65.         
66.          rect(i , j, sheild, sheild);
67.          matches = 1;
68.           
69.         }
70.         else if(matches != 1 ){
71. 
    
72.           fill(0,255,0);
73.           
74.           rect(i , j, sheild, sheild);
75.           
76.         } //close if
77.       
78.       }//close if
79. 
    
80.     
81. 
    
82.     }//close j loop
83.   }//close i loop
84. 
    
85. }//close draw
86. 
    
87. void mouseClicked(){
88. 
    
89.   println( "(x, y) = " + "("   + mouseX  + "," + mouseY + ")" );
90.   for(int i = 0; i < 4; i++){
91. 
    
92.     square[i].clicked();
93.     
94.   }//close for loop
95. 
    
96. }//close mouseClicked
97. 
    
98. void mouseMoved(){
99. 
    
100.     uncoverX[inc] = mouseX;
101.     uncoverY[inc] = mouseY;
102. 
     
103.     inc += 1;
104.      
105.     if(inc > strength - 1){
106. 
     
107.       inc = 0;
108.      
109.     }//close if
110. 
     
111. }//close mouseMoved

2. //this is the class that is the shape you press
3. 
   
4. class Token{
5. 
   
6.   //tracks if the Token has been clicked
7.   int clicked;
8. 
   
9.   //these variable assign a size to the rect
10.   int rectWidth;
11.   int rectHeight;
12. 
    
13.   //these variables give a random location to the rect
14.   int varWidth;
15.   int varHeight;
16. 
    
17.   color c;
18. 
    
19.   //these variables set the bounds for the mouse button
20.   int leftLimit;
21.   int rightLimit;
22.   int topLimit;
23.   int bottomLimit;
24. 
    
25.   Token(){
26. 
    
27.     //tracks if the Token has been clicked
28.     clicked = 0;
29. 
    
30.     //these variable assign a size to the rect
31.     rectWidth = 20;
32.     rectHeight = 20;
33. 
    
34.     //these variables give a random location to the rect
35.     varWidth = int(random(20, width - 20));
36.     varHeight = int(random(20, height - 20));
37. 
    
38.     c = color(255,0,0);
39. 
    
40.     //these variables set the bounds for the mouse button
41.     leftLimit = varWidth;
42.     rightLimit = varWidth + rectWidth;
43.     topLimit = varHeight;
44.     bottomLimit = varHeight + rectHeight;
45. 
    
46.   }//close constructor
47. 
    
48.   void display(){
49. 
    
50.     //rect attributes
51.     fill(c);
52.     noStroke();
53.     
54.     //display a rectangle
55.     rect(varWidth, varHeight, rectWidth, rectHeight);
56. 
    
57.   }//close display
58. 
    
59.   //Make a mouse over
60.   void clicked(){
61. 
    
62.     if(leftLimit < mouseX && mouseX < rightLimit && topLimit < mouseY && mouseY < bottomLimit && clicked == 0){
63. 
    
64.      // stroke(255);
65.       c = color(255);
66.       score += 1;
67.       println("Your Score = " + score);
68.       clicked = 1;
69.     }//close if
70. 
    
71.   }//close clicked
72. }//close Token class

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