Why I am getting java.util.ConcurrentModificationException even when I am using removeIf?What change is required in my code ?
List<String> namesList = new ArrayList<>();
namesList.add("AA");
namesList.add("BB");
namesList.add("CC");
List<String> createList =null;
namesList.stream()
.map(m-> { namesList.removeIf( m1 -> m1=="AA" ) ; return m; } )
.collect(Collectors.toList())
.forEach(System.out::println);
This is happening as your are modifying the source of the stream which is a non-concurrent ArrayList. The ArrayListSpliterator does not have the CONCURRENT or IMMUTABLE characteristic and it does not support removal during iteration. It is not due to usage of the Collection.removeIf method.
From the docs:
A Spliterator that does not report IMMUTABLE or CONCURRENT is expected to have a documented policy (for example throwing ConcurrentModificationException concerning structural interference detected during traversal.
For this to work you need to have List implementation which supports concurrent removal during iteration like a CopyOnWriteArrayList, whose Spliterator has the IMMUTABLE characteristic.
Anyway, you are not using the map operation correctly if you want to conditionally filter items from the List you should use Stream.filter instead also consider using equals while comparing String objects:
namesList.stream()
.filter(m1 -> !"AA".equals(m1))
.forEach(System.out::println);
.collect there! it is totally redundant. EditedAssuming you are trying to remove the value "AA" from your list, here are your options:
namseList.removeIf(s -> s.equals("AA")) - no need to deal with Streams.namesList.stream().filter(s -> !s.equals("AA")).collect(Collectors.toList());Some points:
.collect() on a Stream followed by forEach(). This can be simplified to simply call forEach() on the Stream object.Strings using ==. This can do what you intend (i.e. compare their values, because of String interning), but it is good practice to compare values using .equals().
.map(m -> {namesList.removeIf(...); return m}) is equivalent to .map(m -> m) (i.e. it does not do anything).You probably want to use something like: List namesList = ... namesList.stream().filter(s -> !s.equals("AA")).forEach(System.out::println);
ConcurrentModificationException
This exception may be thrown by methods that have detected concurrent modification of an object when such modification is not permissible. For example, it is not generally permissible for one thread to modify a Collection while another thread is iterating over it.
This exception occurs because you are modifying the stream source.
namesList.stream().map(m-> { namesList.removeIf( m1 -> m1=="AA" ) ; return m; } )
you can simply call below code:
namesList.removeIf( m1 -> m1=="AA" )
Or As @Andy Turner suggested:
nameList.removeAll(Collections.singleton("AA"));
nameList.remove("AA"); would be simpler again.
nameList.removeAll(Collections.singleton("AA"));.Collections.singleton is a Collection (a Set, more specifically).
namesList.remove("AA")==. Never do that. Useequals()instead.Collections.synchronizedCollection(namesList);