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Comment by resca79 | Hacker News Reader

While I appreciate the tecnological background of this project, I don't like this kind of traslators.

It could be useful if you need to execute Java code in Objective-c runtime, but not if you want develop iPhone/iPad app.

Obj-C is simple, the problems are the iOS frameworks that you need to learn to delivery an iOS App. If you are Java skilled, anyway you need to learn these frameworks, and you will spend your time to traslate the examples(stackoverflow) from obj-c to java

I'm not a xcode fans, but it is a great tool when you use the StoryBoard and all features to test, performance, memory .. etc.

Another point is that with the introduction of the Swift language this traslator loses other value

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The purpose of j2objc is not to address a single platform. It's not to write code in Java in order to deliver an iOS only app. It's to share logic across multiple platforms.

If you combine j2objc and GWT together, you can share code between Web, native Android, and native iOS, while writing the UI in JS, Objective-C with InterfaceBuilder/Xcode, or native Android Views.

If you want to share non-UI code across all three platforms you have these kinds of choices:

* js everywhere (WebView wrapper or embedded JS interpreter on iOS) * C everywhere (emscripten/NaCl on WEB) * Java everywhere (GWT->js for Web, j2objc for iOS)

I can only speak from experience, but option three worked fantastically.

I've often heard this idea about 'sharing logic across multiple platforms'.

I agree that it's a noble goal, but I'm curious about places where that sort of logic is actually common enough to justify the overhead of maintaining a cross-platform library.

Most of the applications on my phone are ultimately native UI skins over web services. There might be some logic in there to handle other features, but in most cases it's tied into OS-native features anyway.

I can see cross-platform libraries being useful for games using GL, maybe for media applications that require formats not supported by the OS, and for applications that do heavy image or audio processing – in short, the sort of thing where the value-add is specifically high-performance processing. Maybe that's enough to justify the existence of these tools, though I'd imagine it's almost always a better option to write your library in C in the first place.

Case in point: Inbox by Gmail. It is not just a thin skin over AJAX calls, but actually a fairly sophisticated client side application.

Does Google Inbox use J2ObjC? You seem to be alluding to that but not explicitly saying it.

Google Inbox is indeed written in J2ObjC:

See https://groups.google.com/forum/#!topic/j2objc-discuss/5lMZN...

> a fairly sophisticated client side application is it actually an full blown IMAP client? Most likely it uses AJAX to fetch JSON from Google's proprietary APIs

It works offline, that should give you a clue that it is not just a request/response app. Yes, it does make requests to Google's servers, but it can run completely offline with no connection as well.

I think you're underestimating the amount of platform-independent code in a typical app.

Looking though a random sample of non-game apps on my iPad, I'd guess that about half would have a significant chunk of code which is not OS-specific, including: Gmail, Spotify, Anki, Google Maps, Facebook, Twitter, Penultimate.

I also don't think that the choice between C and Java as the common language is so clear cut. C would get you some speed benefit but Java has GWT for porting Java to Javascript, and and a huge range of other tools and libraries. In the end I think it would come down to how comfortable your development team was in each language.

(Disclaimer: I'm a Java developer)

> C would get you some speed benefit but Java has GWT for porting Java to Javascript

You can compile C to JavaScript with emscripten[0].

[0]: https://github.com/kripken/emscripten

Emscripten's good for games, but I don't think it's good for an app like Inbox.

Dropbox has some mobile apps that have some fairl complex client-side logic with multithreading (https://tech.dropbox.com/2014/04/building-carousel-part-i-ho...), so they use a cross-platform C++ library with bindings to Obj-C and Java with their Djinni library (https://github.com/dropbox/djinni/)

A lot of apps are just API consumers, but apps with any kind of moderately advanced functionality will require some kind of entity model and business rules that need to be captured. Having those things go out of sync between platforms can be a source of bugs or slower development. For shops invested in Java or with a lot of Java engineers, something like this can be be useful so that the entity model and business rules can be encapsulated in a single code base.

Sharing the business logic makes sense, but I'm not confident that sharing code on web and mobile devices is a good point in terms of performance.

The UI in JS is simple to develop, but you have a lack of performance also

From my experience with servers-side JS code, if your JS is fast enough to run with every server request, it's also fast enough to run on today's mobile processors. Obviously for Client-side code this isn't true, but then again if you want your apps accessible from mobile browsers, you need to have it reasonably optimized anyway.

> Obj-C is simple

Yeah you just need to know C, possibly C++, and smalltalk and be comfortable using the syntaxes for all three simultaneously. For the record though I'm a big fan of C and C++, and I don't really care for Java. I can just see why people who already know Java well would want to use Obj-C as little as possible.

You don't need to learn 3 languages to be skilled in Obj-c

Just for one reason, there are many iOS developers in the world, and at the same time C++ and C developers are few today.

If your imagine of the world is USA, maybe true.

"... C++ and C developers are few today."

In a web/js/Ruby/mobile echochamber that may be true. But in the real world C/C++ is very far from being a minority skillset. Take a look at [1][2][3]. C, C++, and Java are the main languages in use today.

[1] http://www.tiobe.com/index.php/content/paperinfo/tpci/index....

[2] http://langpop.com

[3] http://lifehacker.com/the-top-programming-languages-ranked-b...

You need look at the growing data. Maybe the number of people that know c or c++ are more for the ages of the languages itself. Try to look any statistics about github[1] [2]

[1] http://redmonk.com/dberkholz/2014/05/02/github-language-tren...

[2]http://sogrady-media.redmonk.com/sogrady/files/2014/02/repos...

The bulk of Java/C/C++ source will never see the light of day as they power systems owned by corporations who see them as an asset.

Looking at public repos for stats is like counting the number of tables on planet earth by looking at satellite photos. You never see inside the buildings, just whats outside in parks etc.

Let's take a brief moment to talk about systems software, and infrastructure.

It powers your OS, your VM instance running your flashy new CRUD app, your network protocols, your game engines, your browser, the interpreter or compiler you use to run your high level languages, and much, much more.

Programs such as these need high performance, low level access to hardware, or the ability to manage resources in a custom way. Languages like C, and C++ are very well suited for this. Sure, I wouldn't write a web-app in C++, but then again, I wouldn't write a javascript jit-compiler in javascript (okay maybe in asm.js for kicks).

Personally, when I see the growth of higher-level languages like these, I don't attribute it to the fall of low-level languages, but instead to the availability of new languages good for certain tasks.

In 2014, we have the luxury of being able to write applications at higher levels of abstraction, and this is a good thing. But tools like C, and C++ are still, and will be widely used by anybody who needs to develop something with requirements such as those I have mentioned. Layers of abstraction need to be built on top of something, and that something needs to work efficiently and quickly.

I'd consider that fusion of paradigms to be a huge strength of the language.

I would say smalltalk has little to do with LEARNING objective-c. The gist is:

* Message passing between objects. * A nil object that can accept messages without failing. * Duck typing. * A really shitty call syntax.

What more needs to be known?

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