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Original Post: GroovyOrJRuby
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<td style = 'font-size: larger; font-style: bold'><a href = 'http://martinfowler.com/bliki/GroovyOrJRuby.html'>GroovyOrJRuby</a></td>
<TD valign = 'bottom' width = '15%'><a href = 'http://martinfowler.com/bliki/ruby.html'>ruby</a></TD>
<TD valign = 'bottom' width = '20%'><b>28 November 2007</b></TD>
<TD valign = 'bottom' width = '10%'><a href = 'http://technorati.com/search/http://martinfowler.com/bliki/GroovyOrJRuby.html'>Reactions</a></TD>
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<p>Currently there's quite a debate raging over the relative merits
of Groovy and JRuby as scripting languages running on the Java
virtual machine. Curious minds want to know - which of these
languages will win this upcoming language war? People want to know
which language to pick for a project, or which language to commit to
learn.</p><p>Perhaps the first thing to point out is that it's perhaps rather
unfair to see this as a race between these particular two
horses. Scripting has been available on the JVM for a long
time. Jython, a Java implementation of Python, has been around for
several years. There's plenty of other, more obscure languages,
which I daren't mention for fear of offending all the ones I miss out.</p><p>JRuby has got a lot of attention due to the attention of the Ruby
language generally - attention particularly ignited by the interest
around Rails. We've seen a sharp spike of interest around Ruby and
Rails work at ThoughtWorks, and JRuby adds an extra dimension since
it allows people to deploy Rails applications using their existing
Java infrastructure.</p><p>Groovy gets its attention because it, more than any other
language, is designed to work seamlessly with the JVM, and got a lot
of attention from an early JSR.</p><p>Personally I'd dropped Groovy from my radar a couple of years ago
when its development seemed to bog down. With its 1.0 release and
further interesting positive vibes from some of my colleagues I've
started to pay attention again.</p><p>Lets begin by talking about similarities. Both JRuby and Groovy
(and indeed Jython) are modern OO scripting languages. They combine
the well-chosen terseness of scripting languages with good solid
structures for building larger programs. As such they are suitable
both for classical scripting and for writing larger programs. Both
are comfortable with dynamic type checking, although Groovy does
offer some static facilities too. Both support <a href = 'http://martinfowler.com/bliki/Closures.html'>Closures</a>
which are an important feature for the greater expressiveness that
people want from this kind of language.</p><p>The biggest difference between them is their broader platform
philosophy. Groovy is designed to be a scripting language for
Java. As much as possible its syntax tries to match the equivalent
in Java. (Including such ugly things as the default fall-through in
switch statements.) It also works with Java's class library
directly, although it dynamically adds many methods to Java's
classes, vital in order to make use of things like closures.</p><p>JRuby, however, is a Java implementation of the Ruby
<i>platform</i>. Ruby can run directly on mainstream operating systems with
a C runtime, and is starting to run on .NET's CLR. When you
program in JRuby you primarily use Ruby's libraries which are
implemented in Java, and may also use Java's libraries at your
discretion. If you stick to Ruby's libraries, or at least wrap any
foreign elements, you can run Ruby programs on the C, Java, or (in
time) .NET
runtimes. So you can use JRuby to both run Ruby programs on the JVM
and as a language for scripting the JVM.</p><p>One of the big differences between JRuby and Jython is around the
libraries. One of the tricky aspects of porting this kind of
scripting language to the JVM is that these languages are usually
closely intertwined with libraries implemented in C. Porting these
libraries to Java involves rewriting the libraries in Java. Jython
didn't do much of this, as a result many Python apps can't run in
Jython. However the JRuby implementers decided from early on that their
goal was to run Rails apps, as a result many libraries including all
the Ruby standard libraries needed to be ported.</p><p>The fact that JRuby is a Ruby platform on the JVM means that in
JRuby you have two kinds of objects - JRuby objects and Java
objects. Although there are ways for the two to talk to each other
and to convert there is a difference. There are times when you need
to know whether you're dealing with a Java string or a JRuby
string. With Groovy you don't have that boundary, there are just
Java objects.</p><p>It's too early, or rather too difficult, to say if one language
will win out. Both are pretty young, only just finding their feet on
the JVM. On a more personal level, your choice has a lot to do with what
you expect to do with it. If you are only interested in running on
the JVM, then Groovy could well be the easier choice. You are
working directly with Java's library and object model, and the syntax
requires less getting used to. A strong reason to prefer Ruby is the
fact that it lives in multiple implementations. Ruby is a tool you
can use in a lot of other places. As a long time Rubyist, there's
not much incentive for me personally to get heavily into Groovy,
even though I actually like the language a lot from what I've seen
of it.</p><p>Rails is an important factor. The Java world is hardly
lacking in web frameworks, but Rails is widely liked by those who've
used it. I've not got many reports yet about Grails (the Groovy
knock-off) so can't give a firm opinion on that. But I can imagine
that the ability to deploy web apps with Rails could be a major
factor in making JRuby popular. Something else to look at is the
growth of RSpec as a new spin on testing environments.</p><p>With any platform it's as important to consider the people
involved in the community as much as any technical factors. Good people
can overcome technical weaknesses quickly and a vibrant community is a
potent source for big innovations. <a href = 'http://martinfowler.com/bliki/RubyPeople.html'>RubyPeople</a> have formed
a particularly strong community, which has already spawned things like
Rails, Rake, and Rspec. </p><p>Will either matter to Java? After all Jython's been around for a
long time without making a huge impact on the JVM. Tool support is
frankly pathetic for any of these languages when you compare it to
what you have for Java at the moment.</p><p>I think we're actually at an inflection point with Java. Until
recently the Java cry was One VM and <a href = 'http://martinfowler.com/bliki/OneLanguage.html'>OneLanguage</a>. (As
opposed to the CLR which was one VM and many languages, providing
they're C# or VB.) This seems to be changing as people realize the
limitations of Java and begin to seek out different capabilities. It's
likely the future will see multiple languages closely integrated
within the JVM.</p><p>There are plenty of people who dislike the hype around Rails and
Ruby. But even if you dislike Ruby, the hype has led to a resurgence
of interest in new languages. I doubt if the interest in Groovy
would be anywhere near as great as it is if it wasn't for this hype,
nor would Jython be awaking from its slumbers. The ruby/rails hype
has also generated interest in other exotic JVM languages. The
really nice thing here is that the JRuby people have been
encouraging their dynamic rivals - recognizing that the point
here is to encourage multi-lingual inter-operability and innovation.</p><hr></hr></td>
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