Which method is used to create a stream from a collection in Java?

The stream() method is used to create a stream from a collection, such as a List, Set, or Map, in Java. This method is part of the Collection interface and allows developers to convert a collection into a stream, enabling them to use the powerful operations provided by the Stream API to process the elements of the collection. Once converted into a stream, the elements can be transformed, filtered, or reduced using the various methods available in the Stream API.

Using the stream() method is straightforward and involves simply calling stream() on an existing collection. For example, if you have a List<String> called names, you can create a stream by calling names.stream(). This stream can then be processed using operations like filter(), map(), and collect() to achieve the desired result. The stream() method provides a seamless way to transition from using traditional loops and iterations to a more functional style of programming.

In addition to the stream() method, the Collection interface also provides a parallelStream() method, which creates a parallel stream that can process elements concurrently. This method is useful when you want to take advantage of multi-core processors to improve the performance of your data processing tasks. Both stream() and parallelStream() are essential tools for working with collections in Java in a modern, functional way.