Jav 8 FlatMap Explained Stream API

Posted on the 08 July 2016 by Abhishek Somani @somaniabhi

In this short example , i will explain where we can use flatMap function of java stream api . Suppose you have a multi level list where many objects are stored , and you want to convert it to a single list of objects . We can use flatmap which will flatten the list easily . FlatMap basically first applies the transformation , and then then flatten the result in a single collection .


import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
/**
 * Created by abhishek.somani on 8/7/16.
 */
public class JavarootsFlatMapExample {
    public static void main(String[] args) {
        String[] arr = {"abhishekl","somani"};
        String[] arr2 = {"java","example","1.8","stream"};
        List<List<String>> list = new ArrayList<>();
        list.add(Arrays.asList(arr));
        list.add(Arrays.asList(arr2));
        final List<String> strings = list.stream().flatMap(l -> l.stream()).collect(Collectors.toList());
        System.out.println(strings);
    }
}