Book Image

Java 9 with JShell

By : Gaston C. Hillar
Book Image

Java 9 with JShell

By: Gaston C. Hillar

Overview of this book

The release of Java 9 has brought many subtle and not-so-subtle changes to the way in which Java programmers approach their code. The most important ones are definitely the availability of a REPL, known as JShell, which will make experiments and prototyping much more straightforward than the old IDE-based project-led approach. Another, more subtle change can be seen in the module system, which will lead to more modularized, maintainable code. The techniques to take full advantage of object-oriented code, functional programming and the new modularity features in Java 9 form the main subjects of this book. Each chapter will add to the full picture of Java 9 programming starting out with classes and instances and ending with generics and modularity in Java.
Table of Contents (23 chapters)
Java 9 with JShell
Credits
About the Author
Acknowledgement
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface
Index

Chaining many operations with map and reduce


We can chain filter, map, and reduce operations. The following code adds a new getHighestScoreSumForMinPlayersCount method to the MemoryMobileGameRepository class. The code file for the sample is included in the java_9_oop_chapter_12_01 folder, in the example12_19.java file.

public long getHighestScoreSumForMinPlayersCount(int minPlayersCount) {
    return getAll().stream()
        .filter(game -> (game.playersCount >= minPlayersCount))
        .mapToLong(game -> game.highestScore)
        .reduce(0, (sum, highestScore) -> sum + highestScore);
}

The new method performs a filter chained with a mapToLong and finally a reduce operation. The call to filter generates a Stream<MobileGame> with the instance of MobileGame whose playersCount value is equal or greater than the minPlayersCount value received as an argument. The mapToLong method returns a LongStream, that is, a specialized Stream<T> that describes a stream of long primitives...