My primary language of employment is Java, but it's been a long time since I was on the steep part of the learning curve. One thing I thought I'd throw out there would be to read the Javadoc both for the core api and any other libraries you might be using. It's the Java counterpart to perldoc. I think that would take you a long way.

For example, string splitting? You might look at the documentation for java.lang.String and see it has a split method! Regexes in general? A search from the overview page would reveal the java.util.regex package.

Yes, you're going to be typing a whole lot more :-( If Perl is like Charles Dickins' prose in its expressiveness, Java is more like a third-grader's paper on what they did last summer.

As a general piece of advice, I would recommend imitating other code you can find in your project, or in reputable open-source libraries (say, part of the Apache Group). I think cargo-culting is your friend here, as long as you make sure you understand the code you're copying. This is just my opinion though, so if others have contrasting viewpoints, they might be more convincing.

...for instance what is the equivalent to 'Data::Dumper' ?

Not exactly equivalent... but when I feel like needing Data::Dumper in Java (to get an idea of what some complex data structure contains), I usually use XStream with the JSON backend (which I find a little easier on my eyes than the default XML representation).

The usual

  use Data::Dumper;
  ...
  print Dumper $data;
[download]

then becomes something like

  import com.thoughtworks.xstream.XStream;
  import com.thoughtworks.xstream.io.json.JsonHierarchicalStreamDriver
+;
  ...
  XStream dumper = new XStream(new JsonHierarchicalStreamDriver());
  System.out.println(dumper.toXML(data));
[download]

Not ideal, but better than nothing...

I was hoping somebody would drop in with something like this. I knew my usual method of "Just make every object have a debug_print method that knows how to print itself in a sane way" was not ideal, but hadn't done more than a cursory search for something better. Thanks!

If memory serves, Java supports hashes and regular expressions (my two favorite Perl features). So rewrite an existing Perl script in Java, and get used to the differences. And, sadly, be prepared to writing a lot more code than you used to.

(Be grateful your employer is letting you cross-train. I'm in the middle of a corporate merger that is fairly brutal...)

If your Perl code is so important, you'd better ask to cross train an interested Java dev in Perl so that you aren't a single point of failure for your app.

This arrangement should achieve several positive things:

• provide you with an excellent opportunity to work closely with an experienced Java developer who can offer insights and guidance
• spread the knowledge of Perl in your company, increasing the likelihood that Perl is used when appropriate
• protect your employer from dependence on a single person for a system
• save money by not shipping you off to a Java training class

With your student/mentor person you can have thrilling conversations of the form:

In source file Foo.pm, we are going to do X. In Perl we use the map() and split() functions to do X, blah blah blah. Now, how would you do that in Java?

Any proofs regarding the execution speed difference? I bet there was a lot of improvement over the years in the Java world from the notoriously insanely unusably fat and slow language of late 90s, but there is very little reason for Java to ever be quicker than Perl.

Jenda


Support Denmark! Defend the free world!

but there is very little reason for Java to ever bee quicker than Perl.

I guess with JIT compilation and smart optimizers you can get very good speed improvements, inline method calls and stuff like that. Since perl 5 has not JIT, many possible optimizations can't be made.

But I don't know which is actually faster in what cases. Maybe the Debian language shootout has some answers, but at the moment I'm too tired to interpret the results ;-)

I have been working with a dozen of languages prior to Perl and occasionally I jump back Java when the need arises, i.e. I have to make sense out of some piece of code. It is used a lot in the place I work, not only for web- or fat clients, also for number crunching, i.e. processing large volumes of data.

You will find out that Java is completely different. True Perl has support for OO but you can also write non-OO programs and/or mix it. Java is a full OO language; there is no way around it. You have got to start to think OO. It is best not to compare both languages too much as they are completely different.

Java is fairly easy to learn, the syntax is not too difficult. The performance, in general, is pretty good. With support form companies like SUN, IBM, HP etc. there is a lot of stuff available (good library support and frameworks). A good starting point is the SUN website http://java.sun.com/. They have many good tutorials.

Other than that visit the API and Sun's Tutorials early and often.

Don't worry about it - it's just another language! I'd just like to second the oft-repeated suggestion that you shouldn't write Perl in Java - from personal experience, you'll end up with very messy datastructures which can't be manipulated as easily as they can in Perl. That way lies frustration and hairpulling. Try and pick up the Java idioms, and to really embrace object-oriented programming: it'll make you a better Perl programmer.

I've found that using Google to search directly against the Java API is really good for finding exactly the right method to do something. You might have to try searching by what you want to get done, rather than the name you think the method might have - Java doesn't believe in TMTOWTDI! - and sometimes you'll have to roll your own.

All the best!

Don't worry, it's just another car. Who cares that it doesn't have the automatic shifting you are used to, that it doesn't tell you when the oil or gas is low, when the engine is overheating, that to start it you have to use a crank ...

If you don't already type with all ten, get a course of that, it's gonna pay off.

Jenda


Support Denmark! Defend the free world!

Can't say I have a lot of experience with Java, but I'm hoping to take the headlong plunge shortly, as most of the interesting work at my job is in Java these days (seems to be a bit of a trend...)

A couple of things though - as most others have already said, Java is a fairly easy language to learn. Static typing can be annoying, and you sometimes miss a few of the more powerful idioms of Perl, but that passes quickly. I also sometimes have to remind myself that where I'd normally reach for a data structure in Perl, that Java Way is to use an object hierarchy. (I think it's important to learn the "native" way of coding in a language - I've seen plenty of bad Perl code written by C programmers).

Aside from the language, the learning curve is more about all the tools around Java. You don't *have* to use an IDE, but the vast majority of Java devs do. You might also have to deal with things like Maven, Hudson, Spring, Hibernate, Tomcat and whatever the Flavour of the Month is. On top of that, you might have to get your head around SOA, ESBs, Service Orchestration and Choreography, Beans, POJOs et al. (After a while you might realise Java people like to give important sounding names to things that are relatively simple concepts, albeit with a lot of complexity in the details).

Anyway, have fun :)

use Inline::Java;