The Java Streams API provides a powerful and expressive way to perform data processing operations on collections. One useful feature of the Streams API is the ability to perform windowing operations, which allow you to apply operations to sublists, or “windows”, of elements in a stream.

In this blog post, we will explore how to implement windowing operations using the Java Streams API. We will cover two commonly used windowing operations: sliding windows and tumbling windows.

Sliding Windows

Sliding windows are windows that slide across the elements in a stream, allowing you to process overlapping sublists of elements. To implement sliding windows with the Streams API, you can use the IntStream.range() method in combination with the collect() method:

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

int windowSize = 3;
int slideSize = 1;

List<List<Integer>> windows = IntStream.range(0, numbers.size() - windowSize + 1)
    .mapToObj(i -> numbers.subList(i, i + windowSize))
    .collect(Collectors.toList());

Here, we have a list of numbers and we want to create sliding windows of size 3 with a slide size of 1. We use IntStream.range() to generate the indices of the start positions of each window, and then use mapToObj() to create a sublist for each window. Finally, we collect the sublists into a list of windows.

The resulting windows list will contain the following sublists:

[[1, 2, 3], [2, 3, 4], [3, 4, 5], [4, 5, 6], [5, 6, 7], [6, 7, 8], [7, 8, 9], [8, 9, 10]]

Tumbling Windows

Tumbling windows are non-overlapping windows of fixed size that “tumble” across the elements in a stream. To implement tumbling windows with the Streams API, you can use the IntStream.iterate() method in combination with the limit() method:

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

int windowSize = 3;

List<List<Integer>> windows = IntStream.iterate(0, i -> i + windowSize)
    .limit(numbers.size() / windowSize)
    .mapToObj(i -> numbers.subList(i, i + windowSize))
    .collect(Collectors.toList());

In this example, we have the same list of numbers and we want to create tumbling windows of size 3. We use IntStream.iterate() to generate the start positions of each window by incrementing windowSize in each iteration. We then limit the stream to the number of windows based on the list size. Finally, we create the sublists and collect them into the windows list.

The resulting windows list will contain the following sublists:

[[1, 2, 3], [4, 5, 6], [7, 8, 9], [10]]

Conclusion

Windowing operations are a powerful tool for processing collections of elements in a stream. With the Java Streams API, you can easily implement sliding windows and tumbling windows to perform operations on sublists of elements. By using the IntStream.range() and IntStream.iterate() methods, along with the mapToObj() and collect() methods, you can achieve efficient and concise code for windowing operations.

Implementing windowing operations with the Java Streams API can greatly enhance your data processing capabilities and streamline your code. So give it a try in your next Java project! #Java #StreamsAPI