Hi everyone, I just wanted to share this piece of code, and see if someone has a better approach.

I have 2 ArrayLists of ids (strings in my case) that I need to compare.
In the final application I'm doing 1 of the ids ArrayList comes from xml loaded from a server,
the other one represent some ids of particles already on the screen, so I need to know which one to add or to remove.

Hope it will help someone as I didn't find any code around this:

1. 
   ArrayList<String> A = new ArrayList<String>();
   ArrayList<String> B = new ArrayList<String>();
   
   void setup()
   {
     A.add("1");
     A.add("2");
     A.add("3");
     A.add("4");
     A.add("5");
     A.add("7");
   
     B.add("1");
     B.add("2");
     B.add("3");
     B.add("4");
     B.add("5");
   
     findIndexes(A,B);
    
   }
   
   // Returns ArrayList [[TO ADD],[ TO REMOVE]]
   
   ArrayList findIndexes( ArrayList _A, ArrayList _B )
   {
     ArrayList _A_ = _A;
     ArrayList _B_ = _B;
     ArrayList<ArrayList> output = new ArrayList<ArrayList>();
     ArrayList<String> toadd = new ArrayList<String>();
     ArrayList<String> toremove = new ArrayList<String>();
    
     Boolean checkd = false;
     Boolean revert = false;
     int i,j;
    
     if(_A.size()<_B.size())
     {
        _A_ = _B;
        _B_ = _A;
        revert = true;
     }else{
       revert = false;
     }
   
     // what changed in _A_
     for(i=0;i<_A_.size();i++){ 
       checkd = false;
       for(j=0;j<_B_.size();j++){ 
         if(_B_.get(j)==_A_.get(i))checkd = true;
       }
       if(!checkd){
           toadd.add((String)_A_.get(i));
       }
     }
    
     // what changed in _B_
     for(i=0;i<_B_.size();i++){ 
       checkd = false;
       for(j=0;j<_A_.size();j++){ 
         if(_A_.get(j)==_B_.get(i))checkd = true;
       }
       if(!checkd){
           toremove.add((String)_B_.get(i));
       }
     }
     if(revert){
       output.add(toremove);
       output.add(toadd);
     }else{
       output.add(toadd);
       output.add(toremove);
     }
    
     println(output);
    
     return output;
    
   }
   
   void draw()
   {
    
   }