public ArrayList < Object > objectList; 
public ArrayList < Object > backingList; 
public boolean change = false; 

public void onTimer( ) 
{ 

	if ( change ) { backingList = new ArrayList < Object > ( objectList ); change = false; } 
	for ( Object object : backingList ) object.update( ); 

}
 
// ==> this method is invoked while onTimer is running 

public void addObject ( Object objectX ) 
{ 

	change = true; 
	objectList.add( objectX ); 

}