Java 8 Stream flatmap method example.

In a very simple note, Stream.flatMap() is used to convert a Stream of Stream into a list of values.

The flatMap() operation has the effect of applying a one-to-many transformation to the elements of the stream, and then flattening the resulting elements into a new stream.

This page gives a simple example on getting count of distinct elements in a file. In this example, each line represents a stream, each steam(line) is broken into words which represents again a independent stream. Now all these multiple streams will be aggregated to a single stream using flatMap method.

package com.java2novice.streams;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.Arrays;

public class StreamFlatMapEx {

	public static void main(String a[]) {

		try {
			long noOfWords = Files.lines(Paths.get("C:\testfile.txt"))
									.flatMap(l->Arrays.stream(l.split(" +")))
									.distinct()
									.count();
			System.out.println("noOfWords: "+noOfWords);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

Java 8 Streams Examples

1. How Java 8 Streams work?
2. Java 8 Streams parallelism introduction.
3. Explain non-interference behavior of Java 8 Streams.
4. Create Java 8 Stream using Stream.of() method example.
5. Create Java 8 Stream using List example.
6. Create Java 8 Stream using Stream.generate() method.
7. Java 8 Stream.filter() example.
8. Java 8 Stream.map() example.
9. Java 8 Stream flatmap method example.
10. Java 8 Stream peek method example.
11. Java 8 Stream distinct method example.
12. Java 8 Stream sorted method example.
13. Java 8 Stream limit method example.
14. Java 8 Stream forEach method example.
15. Java 8 Stream toArray method example.
16. Java 8 Stream reduce method example.
17. Java 8 Stream collect method example.
18. Java 8 Stream concat method example.
19. Java 8 Stream anyMatch(), allMatch() and noneMatch() example.
20. Java 8 Stream findFirst(), findAny() example.
21. Primitive type Stream example.