Functionalities & Uses of Java Stream Collectors

March 15, 2023
Functionalities Uses of Java Stream Collectors

Java 8 introduced a series of new features to take app development up a level, including new abstraction methods like Stream. It is now possible to process complex data sets declaratively. More so, Java Stream Collector is another function that makes data processing simple and can sum, average, and conduct trivial yet necessary operations.

In tandem, they offer functionalities like searching, filtering, concatenation, etc. Not to forget, Java Stream also conduct parallel computation independently in multi-threaded complex architectures.

With that, let’s dig deep into the most talked feature of Java 8, and explore its functionalities, uses, and more.

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Introduction to Java Stream API

The java.util.streammakes processing a sequence of elements as easy as one-two-three. The best way to perceive the function is as a generalization of lists. However, it is essential to note Java Stream is not an independent data structure. Instead, it is a data wrapper used as a conduit to access and retrieve data, like lists, collections, arrays, sets, etc.

Java has multiple streams, each for a distinct type, like LongStream, IntStream, and DoubleStream. The operations could be either terminal or intermediate. The former sends back either a non-stream object or a void, while the latter outputs another stream.

Uses & Functionalities of Java Stream

Java Stream Collector speeds up and simplifies processing data sets to achieve higher efficiency. This feature helps us process streams via a single line of code. For instance, here is a one-liner to find element ‘x’ within a stream.

boolean doesContainX =>element.contains("x"));

A similar code could also process operations like noneMatch() and allMatch(). The trick is to replace anymatch() with the desired method. Here’s how.

boolean doesContainX =>element.contains("x"));

boolean doesContainX =>element.contains("x"));

Each line outputs a Boolean value as per the conditions defined. Through this, it is now simple to process a wide array of operations, such as filter and match, which previously required iterations.

For instance, here is a one-liner that filters elements with the char ‘x’ and places them in a separate stream.

Stream <String> stream =>element.contains("x"));

All these codes output another stream object, making them intermediate operations. It is a must to remember that Java Stream allows programmers to chain such operations per desire, enabling them to apply multiple filters across streams.

Further, it is also possible to shorten the stream values. For this, the reduce() method comes into play. How does it work?

First, the method labels the start value and accumulator functions as arguments. Then, it applies the latter iteratively, beginning from the start value. And Voila! Final Result.

Exploring Java Stream Collector

Java Stream Collector or Stream.collector() belongs to the second class of operations (i.e., terminal operations). Thus, it is often the final step in the process. Using it requires importing the Collectors Class, done via static import.

import static*;

The above code imports the entire Collector Class. However, one can also import individual collectors rather than a class. Then, a series of collector functions can help collect streams in a desired form.

For instance, a function toSet() collects a stream defined into a set object. Say you have a list titled selectedList. Here is a one-liner to process it.

Set <String> resultSet =;

A similar code works for functions such as toList() and the like. Moreover, we have a function toCollection() at our disposal for better implementation. Use it and then define your preferred collection.

For instance, here is a one-liner to store selectedList stream in a Queue.

Queue <String> result =

A similar code works for other implementations like LinkedList, Deque, Stack, etc.

Java Stream Collectors are also perfect for collecting statistical manipulations. Say you have a List of integers and want to collect their sum. Here, you can either use the reduce() method or summingInt Collector like below.

int sum = -> x));

The above code processes a list of integers and uses the terminal method to collect, sum, and store.

In addition, there are predefined codes for processing other statistical functions, like calculating an average. That said, collectors like summarizing int(), summarizing double(), and summarizing long() also get you an apt summary. The output entails maximum value, minimum value, average, count, and the sum of the data present.

The Final Word

Java Stream API coupled with Java Stream Collectors turns into a power combo, enabling developers to simplify trivial operations and make data processing a breeze. Through this, it is no longer a bore to manipulate and explore data sets. Master Java Collectors, and you can rest assured no data will become hard to handle.

Also Read: Using Java Streams In Java 8 With Examples

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