java - Listiterator in Android Game -

i have 2 arraylist's using, 1 enemy sprites , other bullets. when run app crashes on emulator , within few levels crashes on device upon collision. log keeps telling me have simple listiterator error. wanted know how implement listiterator. have not been using listiterator, searched around find information , examples bit confused on how it. add() function called in ontouch method of view class , collision takes place inside of thread class in own collision methods.

log:

07-20 19:57:46.604: error/androidruntime(234): uncaught handler: thread thread-9 exiting due uncaught exception 07-20 19:57:46.613: error/androidruntime(234): java.util.concurrentmodificationexception 07-20 19:57:46.613: error/androidruntime(234):     @ java.util.abstractlist$simplelistiterator.next(abstractlist.java:64) 07-20 19:57:46.613: error/androidruntime(234):     @ com.android.hitmanassault.hitmanview$hitmanthread.startgame(hitmanview.java:333) 07-20 19:57:46.613: error/androidruntime(234):     @ com.android.hitmanassault.hitmanview$hitmanthread.gamestart(hitmanview.java:290) 07-20 19:57:46.613: error/androidruntime(234):     @ com.android.hitmanassault.hitmanview$hitmanthread.updategame(hitmanview.java:393) 07-20 19:57:46.613: error/androidruntime(234):     @ com.android.hitmanassault.hitmanview$hitmanthread.run(hitmanview.java:237) 

checks collision:

private void startgame(){             synchronized(msurfaceholder){                 for(beam bullet: beam){                     for(sprite sprite: sprites){                         if(checkcollision(sprite, bullet)){                             sprites.remove(sprite);                             beam.remove(bullet);                             mscore = mscore + 1;                             break;                         }                                    }                 }             }                } 

collision method:

public boolean checkcollision(sprite sprite, beam bullet){              boolean retvalue = false;             int spritex = sprite.getx();             int spritey = sprite.gety();             int spritexs = sprite.getx() + sprite.getwidth();             int spriteys = sprite.gety() + sprite.getheight();               int beamx = bullet.getx();             int beamy = bullet.gety();             int beamxs = bullet.getx() + bullet.getbitmap().getwidth();             int beamys = bullet.gety() + bullet.getbitmap().getheight();               if ((beamx >= spritex && beamx <= spritexs) || (beamxs >= spritex && beamxs <= spritexs)) {                 if ((beamy >= spritey && beamy <= spriteys) || (beamys >= spritey && beamys <= spriteys)) {                     retvalue = true;                 }             }                return retvalue;         } 

if add element list while thread iterating list, concurrentmodificationexception.

you can try concurrentlinkedqueue, depending on requirement on consistency model of game, should rethink architecture.

this problem.

for(sprite sprite: sprites) { <------- iterate     if(checkcollision(sprite, bullet)) {         sprites.remove(sprite); <-------- modify ... 

quick fix gather element want remove remove them after loop.

arraylist<beam> toberemovebeams = new arraylist<beam>(); arraylist<sprite> toberemovesprites = new arraylist<sprite>(); for(beam bullet: beam){     for(sprite sprite: sprites){         if(checkcollision(sprite, bullet)){             toberemovebeams.add(beam);             toberemovesprites.add(sprite);             mscore = mscore + 1;             break;         }                    } } beam.removeall(toberemovebeams); sprites.removeall(toberemovesprites );