Parallel Looping Constructs in Java (revisited)

Two years ago, I blogged about parallel for each construct using a very early version of lambda prototype compiler. At that time, Data Parallelism was already available in C# TPL, but Java designers were hard at work in bringing this idiom to Java.

Parallel.ForEach(students, student => {
student.GradePointAverage = student.Tests.Select(test => test.Grade * test.Weight).Sum();
} );

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Lambda expressions support in Java 8 is here for everyone to give it a spin. Functional touch to Collections library makes it a breeze to program in Java. you get this one-liner using Java 8 Stream API.

students.parallelStream().forEach(student -> {
student.GradePointAverage = student.Tests.parallelStream().mapToDouble(test -> test.Grade * test.Weight).sum();

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There are more such one-liners you can think of using parallel constructs in Java 8. Here is another teaser, send an email blast to all customers.

addresses.parallelStream().forEach(address -> sendMail(address));

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Streams API brings several of the LINQ as well as PLINQ awesomeness to Java Collections library. Here is an adhoc query over a collection using the new Streams API.

// Print the names of albums that have at least one track rated four or higher, sorted by name.
.filter(a -> -> (t.rating >= 4)))
.sorted(comparing((Album album) ->
.forEach(album -> System.out.println(;
// Merge tracks from all albums
List<Track> allTracks =
.flatMap((Album album) ->
// Group album tracks by rating
Map<Integer, List<Track>> tracksByRating =

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Check it out here for more one-liners. You may want to checkout this article that compares LINQ with Java Streams API. While, there are constraints with the Java Streams proposal, it hits the right balance and there is a pedagogical value to it as well, keeping majority Java developers happy.


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