Have you used the sequential method within the Streams API?

The sequential() method in the Streams API is used to explicitly switch a stream to sequential mode if it was parallel. By default, streams are created sequentially, but if you called parallel(), you can use sequential() to revert to sequential processing.

Example:

List<String> list = Arrays.asList("a", "b", "c", "d");

list.parallelStream() // create a parallel stream
    .sequential()      // switch back to sequential
    .forEach(System.out::println);

This is useful when some operations should be performed in parallel, and others sequentially, to avoid issues with state or processing order.