Comments on: Making Java “Groovier” with LambdaJ

By: Steve

Steve — Mon, 12 Oct 2009 17:25:38 +0000

I thought this trick would be needed:

Collections.emptyList() can not be used in the ternary as I have it without casting the return result so create a private function that returns Collection.emptyList() to replace the inline call.

By: Sakuraba

Sakuraba — Mon, 12 Oct 2009 07:00:28 +0000

While I like Closures and they way groovy decorates existing JDK classes with them, I think that most of the “hard-to-read”-ness in the original code stems rather from too long class/variable names and crappy formatting than from the absence of Closures.

By: Steve

Steve — Mon, 12 Oct 2009 05:07:01 +0000

Matt,

I think you can do what you want with just the core Java classes. First, I would make it an error for businessActivityBinMetaClassList to ever be null. You could use Collections.emptyList() instead.

You would create a utility class:

class FunctionalMap {
Converter func;
FunctionalMap(Converter c) { func = c;}

List map(List src) {
List val = (src.isEmpty()) ? Collections.emptyList() : new ArrayList();
for (I i : src) {
val.add(convert(i));
}
return val;
}
}
and use it like this:

FunctionalMap inToOut = new FunctionalMap(myConverter);

List myOutList = inToOut.map(myData);

Sorry about the formatting. With this approach I think you could even make an implementation using SynchronousQueue instead of a List for continuous conversion using multithreading.

There would be no need for the static method or helper class, just define inToOut where it is needed and call map.

Another approach might be to make FunctionalUtil and have a static map method that takes the converter.

Thoughts?

Steve

By: Mario Fusco

Mario Fusco — Sun, 11 Oct 2009 21:07:34 +0000

Hi Matt,

sorry but I never tried to use lambdaj from a Groovy test class, so at the moment I don’t have a clear idea of what is going wrong. It seems that for some reason Groovy doesn’t work well with the cglib proxies generated by lambdaj and if this is the problem I am afraid there is no solution for it.

However could you send to my email the code you are using, so I can reproduce this issue by myself?

Just for curiosity did you try my solution from a plain Java test class? Does it work in that case?

Bye
Mario

By: Matt

Matt — Sun, 11 Oct 2009 19:46:17 +0000

Mario,

Thanks for your response! This looks great. However, I’m having some problems getting it to run from my Groovy test class….here’s the result:

Caught: groovy.lang.MissingMethodException: No signature of method: $java.lang.Iterable$$EnhancerByCGLIB$$d94f4d3d.getSrmMetaClassId() is applicable for argument types: () values: []
at CollectExamples.getSrmMetaClassIdListLambdaJTwo(Collect.groovy:36)
at Collect.run(Collect.groovy:87)

Not sure what I’m doing wrong…any ideas?

Thanks,

Matt

By: Mario Fusco

Mario Fusco — Sat, 10 Oct 2009 13:45:27 +0000

Hi Matt,

My name is Mario Fusco and I am the main developer of the lambdaj project. Thanks a lot for your interest in my project. Actually your example could be a lot improved as it follows:

public static List getSrmMetaClassIdListJava(List businessActivityBinMetaClassList) {
. return (businessActivityBinMetaClassList != null) ?
filter(notNullValue(), extract(businessActivityBinMetaClassList, on(BusinessActivityBinMetaClass.class).getSrmMetaClass().getSrmMetaClassId())) :
new ArrayList();
}

So you can achieve what you need with just one line of code and without having any inner class. Indeed lambdaj does all the null checks for you. Almost better than Groovy, isn’t it
Let me know if it works.

Cheers
Mario