Articles related to : javastreams

Creating a Map object from Stream elements using Collectors.groupingBy() allows for a lot of flexibilit

Creating Map with keys and values based on the elements emitted by a stream is easy, if one uses the ready-to-use collectors from Collectors class. Let’s start with the simplest of map collectors toMap().

Creating List or Set object or any collection from stream elements is easy. Just call collect() operation and pass the corresponding collector, generated by one of the factory methods of the Collectors class.

The collect(Collectors.counting()) is a very straightforward operation. It counts a number of emitted elements. But it does a bit more than the Stream operator count().

In this post, we will discuss and demonstrate usage of the ready-to-use collectors that calculate some statistics of the stream elements – count, sum, average, min, and max element of the stream.

Sometimes we need to create a string that contains comma-separated values emitted by a stream. The collect() operation with the Collectors.joining() collector (with a parameter that describes a delimiter) is very convenient way to do it.

Collectors.maxBy() and Collectors.minBy() collectors calculate the max and the min element correspondingly according to a given Comparator

The collect() operation is a specialization of reduce(). It allows implementing a vast variety of algorithms using the ready-to-use implementations of collectors located in the java.util.stream.Collectors class.

The reduce() operation accumulates stream elements into one resulting value, thus “reducing” the stream of values to one value of the same or a different type.

The toArray() operation collects the emitted stream values into an array no matter whether the stream is parallel or not. The only limitation is that the stream has to be finite. Otherwise, the processing never ends.