ConcurrentModificationException thrown on iterator.remove()

Code:java

 
Iterator<String>itr = grass2.iterator();
while(itr.hasNext())
{
String f = itr.next();
String[]c = f.split(":");
int fx = Integer.parseInt(c[0]);int fy = Integer.parseInt(c[1]);int fz = Integer.parseInt(c[2]);
p.getWorld().getBlockAt(new Location(p.getWorld(),fx,fy,fz)).setTypeId(2);
grass2.remove(f);
grass.add(f);
itr.remove();
}
 

It throws ConcurrentModificationException on itr.remove(). I tried to use a for loop before that looked like this:

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Code:java

 
for(String f: grass2)
{
String[]c = f.split(":");
int fx = Integer.parseInt(c[0]);
int fy = Integer.parseInt(c[1]);
int fz = Integer.parseInt(c[2]);
p.getWorld().getBlockAt(new Location(p.getWorld(),fx,fy,fz)).setTypeId(2);
grass2.remove(f);
grass.add(f);
}

But I got the same exception on
for(String f: grass2)

Here's the entire method:

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Code:java

@EventHandler(priority = EventPriority.HIGHEST)
public void kayaVictim(PlayerMoveEvent e)
{
final List<String>grass2 = new ArrayList<String>();
final Player p = e.getPlayer();
Location l = p.getLocation();
World w = p.getWorld();
int x = (int)l.getX();int y = (int)l.getY()-1;int z = (int)l.getZ();
Iterator<String>itr1 = grass.iterator();
while(itr1.hasNext())
{
String f = itr1.next();
if ( !hasKit(p.getName(), Kit.KAYA)&&(
coords( new Location(w,x+0,y,z)).equals(f)||
coords( new Location(w,x+1,y,z)).equals(f)||
coords( new Location(w,x+2,y,z)).equals(f)||
coords( new Location(w,x-1,y,z)).equals(f)||
coords( new Location(w,x-2,y,z)).equals(f)||
coords( new Location(w,x+0,y,z+1)).equals(f)||
coords( new Location(w,x+1,y,z+1)).equals(f)||
coords( new Location(w,x+2,y,z+1)).equals(f)||
coords( new Location(w,x-1,y,z+1)).equals(f)||
coords( new Location(w,x-2,y,z+1)).equals(f)||
coords( new Location(w,x+0,y,z+2)).equals(f)||
coords( new Location(w,x+1,y,z+2)).equals(f)||
coords( new Location(w,x+2,y,z+2)).equals(f)||
coords( new Location(w,x-1,y,z+2)).equals(f)||
coords( new Location(w,x-2,y,z+2)).equals(f)||
coords( new Location(w,x+0,y,z)).equals(f)||
coords( new Location(w,x+1,y,z)).equals(f)||
coords( new Location(w,x+2,y,z)).equals(f)||
coords( new Location(w,x-1,y,z)).equals(f)||
coords( new Location(w,x-2,y,z)).equals(f)||
coords( new Location(w,x+0,y,z-1)).equals(f)||
coords( new Location(w,x+1,y,z-1)).equals(f)||
coords( new Location(w,x+2,y,z-1)).equals(f)||
coords( new Location(w,x-1,y,z-1)).equals(f)||
coords( new Location(w,x-2,y,z-1)).equals(f)||
coords( new Location(w,x+0,y,z-2)).equals(f)||
coords( new Location(w,x+1,y,z-2)).equals(f)||
coords( new Location(w,x+2,y,z-2)).equals(f)||
coords( new Location(w,x-1,y,z-2)).equals(f)||
coords( new Location(w,x-2,y,z-2)).equals(f)||
//
coords( new Location(w,x,y,z+0)).equals(f)||
coords( new Location(w,x,y,z+1)).equals(f)||
coords( new Location(w,x,y,z+2)).equals(f)||
coords( new Location(w,x,y,z-1)).equals(f)||
coords( new Location(w,x,y,z-2)).equals(f)||
coords( new Location(w,x+1,y,z+0)).equals(f)||
coords( new Location(w,x+1,y,z+1)).equals(f)||
coords( new Location(w,x+1,y,z+2)).equals(f)||
coords( new Location(w,x+1,y,z-1)).equals(f)||
coords( new Location(w,x+1,y,z-2)).equals(f)||
coords( new Location(w,x+2,y,z+0)).equals(f)||
coords( new Location(w,x+2,y,z+1)).equals(f)||
coords( new Location(w,x+2,y,z+2)).equals(f)||
coords( new Location(w,x+2,y,z-1)).equals(f)||
coords( new Location(w,x+2,y,z-2)).equals(f)||
coords( new Location(w,x,y,z+0)).equals(f)||
coords( new Location(w,x,y,z+1)).equals(f)||
coords( new Location(w,x,y,z+2)).equals(f)||
coords( new Location(w,x,y,z-1)).equals(f)||
coords( new Location(w,x,y,z-2)).equals(f)||
coords( new Location(w,x-1,y,z+0)).equals(f)||
coords( new Location(w,x-1,y,z+1)).equals(f)||
coords( new Location(w,x-1,y,z+2)).equals(f)||
coords( new Location(w,x-1,y,z-1)).equals(f)||
coords( new Location(w,x-1,y,z-2)).equals(f)||
coords( new Location(w,x-2,y,z+0)).equals(f)||
coords( new Location(w,x-2,y,z+1)).equals(f)||
coords( new Location(w,x-2,y,z+2)).equals(f)||
coords( new Location(w,x-2,y,z-1)).equals(f)||
coords( new Location(w,x-2,y,z-2)).equals(f))
)
{
String[]c = f.split(":");
int fx = Integer.parseInt(c[0]);
int fy = Integer.parseInt(c[1]);
int fz = Integer.parseInt(c[2]);
w.getBlockAt(new Location(w,fx,fy,fz)).setTypeId(0);
grass.remove(f);
grass2.add(f);
itr1.remove();
}
this.getServer().getScheduler().scheduleSyncDelayedTask(this, new Runnable()
{
public void run()
{
Iterator<String>itr = grass2.iterator();
while(itr.hasNext())
{
String f = itr.next();
String[]c = f.split(":");
int fx = Integer.parseInt(c[0]);int fy = Integer.parseInt(c[1]);int fz = Integer.parseInt(c[2]);
p.getWorld().getBlockAt(new Location(p.getWorld(),fx,fy,fz)).setTypeId(2);
grass2.remove(f);
grass.add(f);
itr.remove();
}
}
}, 60L);
}
}

If you're wondering what this does, it makes it so whenever someone who doesn't have the Kaya kit will activate Kaya's fake grass blocks making them turn to air for a few seconds. This can be used for traps and stuff. Everything works fine except it throws that exception every time a fake grass block is activated. Any idea how I can avoid that?

 

ocomobock
In the code you pasted, on line 9 you are still calling grass2.remove();

 

What should I do about that then? I need that there for it to work.

EDIT: Turns out I don't need to add that. It seems to be working, thanks