Java 8 Stream flatMap Sample
Java 8 Stream flatMap operation will return a stream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element.
In simpler terms, a flatMap() is used to convert a Stream of Stream into a list of values. Another way to say it is that flatMap() will flatten a Stream of Stream of values into just a Stream of values.
The Stream.flatMap() sample code below will flatten a Stream of List (Strings) objects into just a Stream of Strings.
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
public class JavaFlatMapSample {
public static void main(String[] args) {
List<String> bigWidgets = Arrays.asList("BigWidgetA", "BigWidgetB", "BigWidgetC");
List<String> medWidgets = Arrays.asList("MediumWidgetA", "MediumidgetB", "MediumWidgetC");
List<String> smallWidgets = Arrays.asList("SmallWidgetA", "SmallWidgetB", "SmallWidgetC");
List<List<String>> allWidgets = new ArrayList<>();
allWidgets.add(bigWidgets);
allWidgets.add(medWidgets);
allWidgets.add(smallWidgets);
List<String> jcdFlatMapList = allWidgets.stream()
.flatMap(widgetList -> widgetList.stream())
.collect(Collectors.toList());
System.out.println("Widget List:");
System.out.println(jcdFlatMapList);
}
}
Output:
Widget List: [BigWidgetA, BigWidgetB, BigWidgetC, MediumWidgetA, MediumidgetB, MediumWidgetC, SmallWidgetA, SmallWidgetB, SmallWidgetC]
I think you will find the Stream.flatMap() operation of Java 8 to be very useful in your everyday Java programming activities.
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Seymour
I have been a software developer for twenty years now focusing on writing high quality Java applications. I try to post useful Java code samples and Java code tutorials on a daily basis. Java is definitely my favorite programming language to develop in.