What does the method parallelStream do?

The parallelStream() method in Java creates a parallel stream from a collection or other data source, allowing operations on elements to be performed concurrently in multiple threads.

Main features:

• Uses ForkJoinPool.commonPool() to distribute tasks among threads.
• Enables faster processing of large data volumes through parallelism.
• Operations such as map, filter, reduce, and others are executed in parallel.

Example:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
int sum = numbers.parallelStream()
                 .mapToInt(Integer::intValue)
                 .sum();
System.out.println("Sum: " + sum);

In this example, summing the list elements occurs in parallel, which can improve performance on multi-core processors.

It is important to note that parallel streams are not suitable for all tasks — if operations are not independent or require strict order, using parallelStream() may lead to errors or decreased performance.