Learning Java so I can get at clojure [closed]

Question

I have a history of hating Java, having used it pretty regularly in the late 90's during the 'slow as balls' era. As such, I never really learned it well. From what I understand, Java is actually a pretty good language to use these days. I've been thinking about diving into it because of Jython and Clojure. That is to say, I'd like to program in Java and use inline Jython or Clojure where appropriate. But truthfully, I'll probably just be programming in Jython/jRuby and calling up clojure from there.

Which brings me to my question. I know both of these languages can be called from Java, but is that necessarily good practice? Should I even bother learning java if I just want to use Jython as the primary language? Seeing as how that's a large part of my motivations here, I'd like to know that I'm not terribly misguided before jumping in. I'm aware there is a very high risk for projects to become a kludge if done in multiple languages like this.

I'm still learning about the JVM and the like, so I apologize if this question is painfully obvious.

Answer 1

Jython can be viewed as a cross compiler from Python to the Java Virtual Machine. As such, to get the most out of Jython you'll obviously have to learn Python, and probably will need to learn Java.

You can skip some of the Java learning, but at the end of the day, Java and the JVM grew up together. That means that Java code tends to lend understanding of the JVM. It is possible to gain understanding of the JVM without Java, but that's not a path well travelled. Any Jython code that imports a Java library will immediately have you searching Java documentation, so if you avoid leaning Java you're going to learn it piecemeal anyway.

You will have to decide if a piecemeal approach or a formal approach is more appropriate for you and your situation. A lot of deciding which path to take is knowing how you learn best.

As far as the "slow as balls" period of the 90's, that's when I was learning Java. Personally, I feel it is better to describe it as "slow as balls if you did incredibly stupid things with Java". Now I think people have built up a sufficient skill set to avoid translating C directly into Java. That said, I do occasionally encounter the 2000+ line method, so perhaps I'm being a bit rosy in my projection. The entire JVM is laid out in such a manner that good object oriented code runs faster, and if you're constantly trying to go to "other" objects for all the data you need locally, you'll just stack thrash the JVM.

Regardless of opinions, the JVM is now the hot Java item. There has been "other language" support by one means or the other for over a decade now; however, the excitement around Domain Specific Languages seems to have sparked an interest in compilation technologies and the JVM. The other languages benefit from the JVM being an easy target to hit with built-in cross platform support, excellent performance, huge availability of libraries, and generally good documentation. Learning Java and the JVM will help you with a lot of the JVM supported languages, as many of them don't flesh out their library space in favour of hooking into a pure Java library.

Answer 2

I'd say it's worth knowing Java even if you plan on only using other JVM languages. I use JRuby and Scala, and have played around with Clojure. If you are building things to run on the JVM, knowing Java is a bit like knowing C when working natively–you don't have to know C, but if you do, you can write the bits that need speed in C and wrap them in a Ruby or Python library or whatnot.

It's worth knowing the basic principles of how Java works in terms of things like interfaces and annotations and how the classpath works because otherwise you are working with basically a leaky abstraction. What happens when your interop isn't very good? This is especially true if you are planning to do Clojure and Jython!

The other reason to know Java is simply because if you are using code in the Java ecosystem, you have to be able to read and write Java. You need to write a library? Yes, you can probably write it in Clojure, but if you want other JVM language users to be able to use it, you should probably have written it in good, idiomatic Java. Scala is close enough to Java for this purpose; Clojure or Ruby or Python, not so much. Just being able to read and comprehend Java programs is very important too.

The other great benefit is simply that you get more libraries and they are better tested. You need a double-ended queue? Check the Java Collections Framework. Good random number generation? java.security.SecureRandom. UIs? Well, Swing, AWT and SWT are... okay, bad example. Knowing the benefits and shortcomings of these only comes from doing some Java programming and learning the various ways not to suck at Java.