Source code for the video example of Stream.flatMap() available at: <https://youtu.be/ouinDyk-H0c>

FlatMapExplained.java

import java.util.Arrays;
import java.util.stream.Stream;

import it.polito.po.data.Lyrics;
/**
 * Explaining how Stream.flatMap() works 
 * with a simple code example...
 * @author mtk
 *
 */
public class FlatMapExplained {

	public static void main(String[] args) {
		String text = Lyrics.ALL_ALONG_THE_WATCHTOWER;
		// let us split this song lyric into words...
		// First of all we have to create a stream
		// out of the String text variable
		
		Stream<String> st = Stream.of(text);
		
		// then we need to split the text into words
		// using the split function of String
		Stream<String[]> swa = st.map( l -> l.split("[ ,.!?]+"));
		
		// though the resulting stream has String[] as elements...
		//..while we would like to have String (its elements)
		
		// we need to flat out the aggregate type into
		// its individual elements.
		// this is exactly what flat map is doing
		Stream<String> sw = swa.flatMap( a -> Arrays.stream(a) );
		
		// Now that finally we have our stream of words
		// we can print it out (e.g.)
		sw.forEach(System.out::println);
	}

}