It's one of the common exception that occurs when you iterate over a collection and try to remove an entry.
Few examples are:
List<String> list = new ArrayList<String>();
list.add("2);
list.add("3");
list.add("4");
for(String s: list){
if(s.equals("2")){
list.remove(s);
}
} and run the snippet, we can see Exception in thread "main" java.util.ConcurrentModificationException.
Now just a little modification, we will use Iterator, since it can allow to remove the element while iterating, so the resultant code looks like
List<String> list = new ArrayList<String>();
for(Iterator<String> it=list.iterator;it.hasNext();){
if(it.next().equals("2"){
it.remove();
}
}
System.out.println("Size of List"+list.size());
Which will give output as 2 :)
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Now the same for HashMap
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("122", 233);
map.put("124", 456);
map.put("125", 345);
for (Entry<String, Integer> entry : map.entrySet()) {
System.out.println(entry.getKey() + " " + entry.getValue());
}
for (Entry<String, Integer> entry : map.entrySet()) {
if (entry.getKey().equals("125")) {
map.remove(entry.getKey());
}
}
Same exception,
Now modify the loop as
for(Iterator<Entry<String, Integer>> iterator= map.entrySet().iterator();iterator.hasNext();){
Entry<String, Integer> next = iterator.next();
if(next.getValue()==456){
iterator.remove();
}
} Its Gone!
