Can you show an example of using the flatMap method in Stream API for collection processing?

The flatMap method in the Stream API is used to transform each element of a stream into another stream and then merge all these streams into one.

This is useful when you have a collection of collections and want to get a single flat stream of all elements.

Example: there is a list of lists of strings, and you want to get a single list of all strings:

import java.util.*;
import java.util.stream.*;

public class FlatMapExample {
    public static void main(String[] args) {
        List<List<String>> listOfLists = Arrays.asList(
            Arrays.asList("apple", "banana"),
            Arrays.asList("orange", "pear"),
            Arrays.asList("grape")
        );

        List<String> flatList = listOfLists.stream()
            .flatMap(Collection::stream) // transform each inner list into a stream and merge
            .collect(Collectors.toList());

        System.out.println(flatList); // [apple, banana, orange, pear, grape]
    }
}

Here, flatMap flattens nested lists into a single stream of elements.