I suppose p is the reference to the PApplet reference in a class or a library...
In this case, you can register your class to be called like keyPressed / keyReleased is.

The only way is to create a boolean by yourself. I found some code after a long search:

1. boolean[] keys = new boolean[4];
2. final int Q = 0;
3. final int A = 1;
4. final int O = 2;
5. final int L = 3;
6.  
7. void setup(){
8. }
9.  
10. void draw() {
11.   if(keys[Q]) println("Left up");
12.   if(keys[A]) println("Left down");
13.   if(keys[O]) println("right up");
14.   if(keys[L]) println("right down"); 
15. }
16.  
17. void keyPressed() {
18.     switch(key) {
19.       case 113: //q
20.           keys[Q] = true;
21.           break;
22.       case 97: //a
23.           keys[A] = true;
24.           break;
25.       case 111: //o
26.           keys[O] = true;
27.           break;
28.       case 108: //l
29.           keys[L] = true;
30.           break;       
31.     } 
32. }
33.  
34. void keyReleased() {
35.   switch(key) {
36.       case 113: //q
37.           keys[Q] = false;
38.           break;
39.       case 97: //a
40.           keys[A] = false;
41.           break;
42.       case 111: //o
43.           keys[O] = false;
44.           break;
45.       case 108: //l
46.           keys[L] = false;
47.           break;       
48.     } 
49. }    

p was indeed the PApplet. (Thought that would be clear since it is common used in library development, but i think some people didn't even notice it was there)

Yep, sorry, i didn't realize it was under library development... So i made this silly reply. Here, there is a say that says: trying to teach the Pope how to pray. I felt just like this :)