Careful with Parallel Streams in java 8

List<String> list = new ArrayList<String>(); //contains about 1000 element

List<String> listA = new ArrayList<String>(); // zezo element now

List<String> listB = new ArrayList<String>(); //zezo element now

list.parallelStream().forEach(e -> {
  if (e.equals("A")) {
    listA.add(e);  } else {
    listB.add(e);  }
});

list.stream().forEach(e -> {
  if (e.equals("A")) {
    listA.add(e);  } else {
    listB.add(e);  }
});

Maybe some guys will think that the above codes with parallelStream() is faster and better than the code with stream()

If you try to run it in fact with parallelStream() then it may throw IndexOutOfArrayException, but with stream() is well.

Why?????

1. listA.add(e); and listB.add() is not supported using in mutilthread. Your code is not good

2. why it throw IndexOutOfArrayException? please read codes of ArrayList :-)

Note: 

1. you should use  

List<String> synlist = Collections.synchronizedList(list);

So you can use synlist in multithread

2. Only use list.get() in multithread, the function is thread safe