Code:

for (int i=0; i<list.size(); i++) {
 int val = list.get(i);
 if (val == valueToRemove) {
   list.remove(i);
   break;
 }
} 

My code was generic, since you didn't show what kind of data you put in the list.
Assuming it holds Integer objects, indeed, you have to do:
int val = (Integer) list.get(i);

yes, it is integer objects.

thankyou very much, works perfectly.

The java ArrayList docs linked to from the Processing reference page includes a list of "Methods inherited from interface java.util.List" including the remove(Object) method...

As for the distinction between int and Integer this goes some way towards explaining it; though doesn't satisfactorily explain why we need these different types.  I think I'll leave that to the Java experts

Thanks for all the help and explanation.

from blindfish's link;
"An Integer, is a Object that contains a single int field. .....It is sort of like a Fedex box to contain the int."

Regarding remove():
I am using this to remove elements in an arrayList called "associates". An element is removed from associates when found.
An arrayList of agents wander around and when they find one of their associates, that associate is removed from their associate list.

println("found-something");
println("id: " + id + ", who: " + who);  
//id is the arrayList of agents, who is the particular agent of that arrayList
println(associates);
found = space[i].home.id;         //id of nest-associate found
//agents are a class, which with another class (home) form a composite class (space).
println("found: " + found);
for (int j=0; j<associates.size(); j++) {
 int val = (Integer) associates.get(j);  
 if (val == found) {
 associates.remove(new Integer(val));    //remove from list
 }
}
println("associates left: " + associates);

Problem:
I want the element to be removed from the arrayList associates of the agent that has found the associate only - so each agent has to find all its associates, removing them from the list as they find them BUT what is actually happeing is that the find is being removed from the associate list of all the agents in the same arrayList.
I hope that makes sense?
Does anyone know why this might be happening? Happy to post any code you might need to help - just not sure what to post!
cheers.

i'm still stuck on this

i think, as blindfish says , i am "setting a reference to the original array rather than creating a true copy".

my code:
ObjectA [] objecta= new ObjectA[objecta];
void setup() {
//data is loaded from an xml file

objecta[i] = new ObjectA(id, color(H, S, B), area, new PVector(position.x, position.y));     //defines ObjectA
 //add associates to arrayList of ObjectA and ObjectB
   objecta[i].associates.add(asso1);
   objecta[i].objectb.associates.add(asso1);
   objecta[i].associates.add(asso2);
   objecta[i].objectb.associates.add(asso2);
}
////////////////////////////////////////////////////////////////////
class ObjectA{
 ObjectB objectb;
 ArrayList objectCs;
 PVector origin;
 ArrayList associates = new ArrayList();
 int objectcCount = population;

 ObjectA(int id, int colour, int Size, PVector loc) {
   objectb= new ObjectB (id, colour, Size, loc);                
   //ObjectC
   objectCs = new ArrayList();
   origin = loc.get();
   for (int i = 0; i < population; i++) {
     objectCs.add(new objectC(id, Size, origin, false, i, associates));
//i think this is were i go wrong passing the associates to objectCs      
   }
 }
////////////////////////////////////////////////////////////////////
class ObjectB {
 int id;
 color colour;
 int Size;
 int x;
 int y;
 PVector position;
 ArrayList associates = new ArrayList();

 ObjectB(int identity, int c, int area, PVector loc) {  
   id = identity;
   colour = c;
   Size = area;
   position = loc.get();
   }
////////////////////////////////////////////////////////////////////
class objectC{
 ArrayList associates = new ArrayList();

objectC(int identity, int Size, PVector loc, boolean mode, int whom, ArrayList asso) {
 associates = asso;
 }

ObjectA is composed of ObjectB and ObjectC. ObjectCs is an arrayList.
how can i copy the arrayList associates of either ObjectA or ObjectB to each ObjectC?

Thanks