Java 8 will go GA in March 2014. java8_logo The first proposed final draft of Java 8 JSR 337 was released early this week. One of the main components of this JSR is Lambda Expressions for the language (JSR 337). This brings the functional constructs to the language, which will undeniably make Java a top contender among other functional peers (Scala, Groovy, Clojure) on the JVM for Java developers. Conciseness is only part of the story, check out how Java 8 programs start to look with Lambda expressions. While being concise for a casual reader, it clearly makes a case why thinking functional may benefit to Java developers in terms of the powerful constructs it offers. The conciseness does not take away readability of the Java program, instead it makes Java developers feel home and enables functional programming with ease, taking away the heavy lifting usually required for moving away from OO paradigm.

I stole the name “” from Neal Ford‘s excellent series of articles about functional languages on the JVM. The latest installment of the series was “ Functional coding styles”. While, the article takes on legacy Java, adding Java 8 to the mix would not hurt. So, let us take his example where you are given a list of names, some of which consist of a single character. You are asked to return the names in a comma-delimited string that contains no single-letter names, with each name capitalized. Here are the various flavors of the implementation taken from the article, while Scala, Groovy and Clojure has its functional version, Java’s implementation is imperative and old school.

Java version:

Scala version:

Groovy version:

Clojure version:

Happy Holidays from the islands

Java 8 version of functional processing

With Java 8, functional interfaces makes this possible with Lambda expressions and Streams make you even more fun when working with Collections in Java 8. Here is the functional version in Java 8.

Switch it to parallelStream() for parallel processing, as simple as that to kick the tires of your cores.

My original intent was to compare with the languages as perceived by Neal Ford in his article. It is unfair to leave behind some of the cool languages on the JVM. Thanks Luke for bringing this up. I strongly believe top-notch IDE support (Eclipse or Intellij) is a win-win situation for users and language implementors. With that context, I updated my list to include Fantom, Gosu, Xtend, Kotlin, Ceylon in order of their age (oldest first).

Fantom version:

Gosu version

Xtend version:

Kotlin version:

Ceylon version:

Personally, I feel Java 8 and Groovy has better success rate in making developers stay in their comfort zone and still enjoy functional prowess. While, I agree Clojure and Scala versions make their case to different set of developers, I believe maintaining a larger code base will be a challenge, when time to develop and market is ever shrinking, and bringing someone up-to-speed with these language tricks will not be easy. If it looks good, eat it, does not play well when it comes to programming in general. While coming to the newer JVM languages, parallelism is one factor that makes Java 8 easy peasy to deal with. These new breed of languages bring ton of cool features (topic for another blog post!) and attracts developers to the JVM, not just Java developers, which is good for the platform. It remains to be seen in the coming years how well these languages get adopted in mainstream development.

Merry Christmas and Happy New Year everyone!

Update (12/29/2013) : Updated the languages comparison to include newer JVM languages: Fantom, Gosu, Xtend, Kotlin, Ceylon.

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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.

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.

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.

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.

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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Java 8 adds support for bulk data operations (JEP 107) in the Collections library. It is unlikely every forms of bulk data operations will be added to the retrofitted Collections framework, but the language designers are making every possible effort in accommodating general use cases of “filter/map/reduce for Java”. Libraries should make use of parallelization on multi-core platforms in order to perform massive parallelizable operations and this means literally kicking-in your cores to its fullest potential. This area of OpenJDK is undergoing heavy changes, it is possible these APIs are changed or improved before milestone 6 when JDK 8 is officially feature complete. But, they are stable enough to give it a spin today. You can grab the lambda build from here. I have been using the latest Intellij 12 preview for my hands on with the new features in Java 8. It actually supports most of the new Java 8 languauge features and intellisense rocks.

The Streams proposal is well thought of and brings the much sought after functional power to Java and you won’t regret upgrading from Java 6 -> Java 8, if you are still hanging around with Java 6 in that time frame. This one is just a preview of what is coming in Java 8.

Let us implement a method to check if a keyword list exists in a tweet. Here is one way to implement it in plain old Java.

Now, that I am taking the Functional programming course, I would like to compare it with Scala, the mature functional language on the JVM. In Scala, this can be implemented as one liners and there are couple different ways to do this, one using exists and other using the foldLeft function, although exists is my favorite as it is clean and less cryptic.

I can understand why functional programmers are more obsessed with “small is beautiful” theme and hate outright verbosity. Now that all dust has settled with Java’s once uncertain future and stalled innovation, its new steward Oracle is betting on to bring back its lost glory in round 2 and you see that happening with Java 8. Finally, the language brings freshness to Java camp in offering functional constructs to Java and make functional programming in Java a breeze. Here is a teaser:

Isn’t nice to have a one liners in Java too? Java is close, but could reduce some noise as you have to call stream() on the Collection which might seem unnecessary. Stream interface supports a fold operation very similar to Scala’s foldLeft function and implements using a similar approach as of Scala.

Now, let us take this example further, filter tweets matching keywords. This was inspired by Week 3 assignment from the “Functional Programming Principles in Scala” course which btw I am enjoying it so far. Again, you can see Java makes it a cut. I am trying to keep it not being a spoiler.

In this example, you notice that you have to use stream() as well as into() operations to get the result of stream processing. I believe this is a limitation with the iteration 2 Streams implementation which was referred as “the bun problem” that we have to live with.

Streams in Java 8 is making implementing bulk operations a no brainer. While it involves some effort in learning the new concepts, it opens up a new dimension to library developers. Thanks to JSR 335 which brings Java up to speed with other cool languages out there in the planet.

For fun, I want to toss in a new exists() API to the Stream interface so I could use it to filter on my keywords list. This can be done with the help of extension methods, another new concept in Java 8.

Basically, I am delegating the implementation to anyMatch() for simplicity as both reveal the same purpose. Here is a custom List implementation that exposes this API on the collection. This is a primitive implementation, which btw I am trying to keep this updated with the recent library changes. I hope there is a better way to do this, but the point is, it enables developers to extend the Streams framework and fill in special cases.

exists() variant of the code is shown below.

There are several new concepts in the library that requires functional mindset to fully benefit from it. You can switch these Streams to use a parallel version, by using parallel() instead of stream() on the Collection. Stream operations are classified as lazy and eager based on their implementation.
I hope to uncover some of these new concepts in the coming months. I wish function types made into Java 8, but that is different story for another day. Enjoy functional programming in Java!

I have covered Lambdas in the past and this excellent JavaZone talk by Angelika Langer should bring you up to speed with the current state of affairs with Lambdas in Java 8. You can also find Maurice Naftalin’s LambdaFAQ useful.

Lambdas in Java 8 from JavaZone on Vimeo.

Update (10/20/2012) : Updated samples to use method reference and built with the latest Lambda build 61. Clarified the bun-problem with streams proposal.
Update (11/20/2012) : Updated MyList implementation to compile with the latest API changes and much cleaner implementation.
Update (2/3/2013) : Updated code to compile with the latest lambda build 75.
Update (6/15/2013) : Updated code to compile with the latest lambda build 94.

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It is nice to download the course materials from and view them offline especially the mp4 video lectures. Here is a nice utility which exactly does that. I used this script to download video lectures for Functional Programming Principles in Scala course. It comes handy to listen from smartphone!

git clone
cd coursera
./coursera-dl progfun-2012-001 -u **** -p *****

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