Java8 Difference between parallel stream and sequential stream

A parallel stream is a stream that is capable of executing operations in parallel, meaning that the operations are divided into smaller tasks and executed concurrently on multiple threads. A sequential stream, on the other hand, is a stream that only executes operations in a single thread.

The main difference between parallel and sequential streams is their performance characteristics. Parallel streams are designed to take advantage of multi-core processors, so they can execute operations much faster than sequential streams for large amounts of data. However, for small amounts of data, the overhead of creating and managing multiple threads can make parallel streams slower than sequential streams.

You can create a parallel stream by calling the parallelStream() method on a Collection or by calling the stream().parallel() method on a stream.

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
Stream<Integer> parallelStream = numbers.parallelStream();

You can also create a sequential stream by calling the stream() method on a Collection or by calling the stream().sequential() method on a parallel stream.

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
Stream<Integer> sequentialStream = numbers.stream();

It’s worth noting that when creating a parallel stream, it does not guarantee that all the operations will be parallelized, it depends on the operations and the size of the data.

It’s also worth noting that not all the operations are parallelizable, for example, the forEach method cannot be parallelized.

In summary, parallel streams are best for operations that can be executed concurrently on large amounts of data, while sequential streams are best for operations that cannot be executed concurrently or for small amounts of data.