http://wiki.processing.org/w/Multiple_key_presses

Thanks! Unfortunetaly, there isn't really much of an explanation, so I'm unsure as to what everything is and does and what it returns. Can someone clear this up for me? Thanks again! 

The idea is to have a boolean for each kind of key you need to manage. When a key is pressed, set its boolean to true. When it is released, set it to false. Check the state of the booleans to know what to do.
Use the functions, not the variables in draw().

Example:

1. int x, y;
2.  
3. void setup()
4. {
5.   size(400, 400);
6.   smooth();
7.   noStroke();
8.  
9.   x = width / 2;
10.   y = height / 2;
11. }
12.  
13. void draw()
14. {
15.   background(255);
16.   fill(#55AAFF);
17.   ellipse(x, y, 20, 20);
18.   if (kh) x--;
19.   if (kl) x++;
20.   if (kj) y++;
21.   if (kk) y--;
22. }
23.  
24. boolean kh, kj, kk, kl;
25. void keyPressed()
26. {
27.   switch (key)
28.   {
29.     case 'h': kh = true; break;
30.     case 'j': kj = true; break;
31.     case 'k': kk = true; break;
32.     case 'l': kl = true; break;
33.   }
34. }
35.  
36. void keyReleased()
37. {
38.   switch (key)
39.   {
40.     case 'h': kh = false; break;
41.     case 'j': kj = false; break;
42.     case 'k': kk = false; break;
43.     case 'l': kl = false; break;
44.   }
45. }