The mapMulti()
method in Java, introduced in JDK 16, is a powerful method of the Stream
interface that allows more complex and flexible mappings of elements. It enables you to map each element of the stream to multiple elements, providing more control compared to flatMap()
.
Table of Contents
- Introduction
mapMulti()
Method Syntax- Understanding
mapMulti()
- Examples
- Basic Usage
- Using
mapMulti()
with Complex Transformations
- Real-World Use Case
- Conclusion
Introduction
The mapMulti()
method allows you to perform a one-to-many mapping of elements, where each element of the original stream can be mapped to zero or more elements. This method is particularly useful for scenarios where you need to produce a dynamic number of results for each input element.
mapMulti() Method Syntax
The syntax for the mapMulti()
method is as follows:
<R> Stream<R> mapMulti(BiConsumer<? super T, ? super Consumer<R>> mapper)
Parameters:
mapper
: ABiConsumer
that consumes an element of the stream and aConsumer
to which multiple elements can be passed.
Returns:
- A new
Stream
consisting of the mapped elements.
Throws:
- This method does not throw any exceptions.
Understanding mapMulti()
The mapMulti()
method allows you to take each element of the original stream and produce multiple elements for the resulting stream. This is achieved by using a BiConsumer
that processes each element and calls a provided Consumer
for each resulting element.
Examples
Basic Usage
To demonstrate the basic usage of mapMulti()
, we will create a Stream
of integers and use mapMulti()
to map each integer to its square and cube.
Example
import java.util.stream.Stream;
public class MapMultiExample {
public static void main(String[] args) {
Stream<Integer> stream = Stream.of(1, 2, 3);
// Use mapMulti() to map each integer to its square and cube
Stream<Integer> mappedStream = stream.mapMulti((number, consumer) -> {
consumer.accept(number * number); // Square
consumer.accept(number * number * number); // Cube
});
// Print the mapped elements
mappedStream.forEach(System.out::println);
}
}
Output:
1
1
4
8
9
27
Using mapMulti()
with Complex Transformations
This example shows how to use mapMulti()
to split a stream of sentences into a stream of words.
Example
import java.util.stream.Stream;
public class MapMultiComplexExample {
public static void main(String[] args) {
Stream<String> stream = Stream.of("Hello world", "How are you");
// Use mapMulti() to split sentences into words
Stream<String> wordStream = stream.mapMulti((sentence, consumer) -> {
for (String word : sentence.split(" ")) {
consumer.accept(word);
}
});
// Print the mapped elements
wordStream.forEach(System.out::println);
}
}
Output:
Hello
world
How
are
you
Real-World Use Case
Expanding Hierarchical Data
In real-world applications, the mapMulti()
method can be used to expand hierarchical data structures, such as expanding a stream of directories into a stream of files.
Example
import java.io.File;
import java.util.stream.Stream;
public class MapMultiFileExample {
public static void main(String[] args) {
Stream<File> directories = Stream.of(new File("dir1"), new File("dir2"));
// Use mapMulti() to expand directories into files
Stream<File> fileStream = directories.mapMulti((directory, consumer) -> {
File[] files = directory.listFiles();
if (files != null) {
for (File file : files) {
consumer.accept(file);
}
}
});
// Print the mapped elements (files)
fileStream.forEach(System.out::println);
}
}
Output:
(Note: The actual output will depend on the contents of the directories.)
Conclusion
The Stream.mapMulti()
method is used for performing one-to-many mappings of elements in a stream. This method is particularly useful for scenarios where you need to produce a dynamic number of results for each input element. By understanding and using this method, you can efficiently manage and process streams of values in your Java applications, allowing for flexible and complex data transformations.
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