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Android to WP7 absolute newbie question: C# or VB?

I'm going to migrate my Android application into WP7 platform. Android one contains heavy enough calculation stuff (encryption/decryption), plus extensive usage of DB (SQLite) and some graphics (simple) and I'm trying to figure which language to select: either C# or VB
I have some experience both in C# and VB.net, but can't decide which one to select, any clues?

I would recommend C#, based on a couple of factors:
I assume the Android application is written in Java. Between C# and VB, C# is the most similar.
If you are doing lots of calculations, C#'s more terse syntax will probably make the code easier to read. VB is more verbose and thus tends to produce more clutter.
Since you are new to the platform, you will definitely find a lot more resources with C# code examples than with VB.

I went from VB.net to C# and wouldn't ever go back through my own choice!
Aside from the technical differences (see here for just one comparison), it's my personal opinion that C# is more readable, fluent and just plain better.
Do a search on google for heaps of comparisons on why one is better than the other. At the end of the day it's your personal preference... try both and see which you prefer.

There are no technical benefits or drawbacks to choosing either language; the complete set of APIs and platform features are available to you whether you choose C# or VB.NET, so it comes down to whichever you are most comfortable with or want to spend more time with.
The only thing that might sway it one way or another is that (in my opinion) there are more samples, blog posts, and general help written in C# than VB.NET, but that's about the only differentiator I can think of.

If you aren't particularly familiar with either then definitely use C#. By far and way the vast majority of code you will come across in the Web and in books on Silverlight will be written C#.

I'd go with C#, it's a far more popular language. Furthermore, Java to C# is an easier transition.
Edit:
Popularity of a language make's it easier to find information and perhaps more importantly, quality developers.

Choose the language you are more comfortable with.

I would suggest c# because it's more similar to java. So maybe you will manage to save code structure.

C# for sure. C# is a lot more alike Java, and syntax alike much more compatible.
Next to that C# is more popular so more resources for it, and because of the extra time they spend on C# the compiler slightly generates higher performance MSIL.

If you know Java you'll find C# very comfortable to transition to and work with, especially if you're having to maintain older Java code as well as working on the new project. I've worked in situations where I had to work with VB6, VB.NET and C# code within the course of a day and it can be tricky to remember not to use or to use semi-colons or that the variable type goes first or last.

About "GUI in C# and code in C++"

First of all, until now, all my programming education, has been targeted to console applications, just like everyone who starts learning C and C++. (the 2 languages i know)
Now, i want to jump to the nice graphical World.
So, I am exploring Windows Forms, i have already got many headaches trying to understand the language that it uses (quite diferent from native C++), but i managed to do a couple of things like using textbox and buttons.
Well, the thing is, i have read in many places that, in order to avoid headaches trying to code winforms in C++, i'd better "Build the GUI in C#, because it's way easier, and the logic, and code in C++". And that is my question, i don't understand that statement, at all.
What is that supposed to mean?
Also, it's C# THAT similar to C++, as to affirm that statement? Cause, if C# was too diferent to C++, i would have to learn the whole C# language
hope you understand my doubt.
PD : Sry about my bad english.

Joan, while it is certainly possible to develop an applications Front End in C# and the logic in C++ I believe it to be a huge waste of effort to do it this way since you only complicate yourself for no real benefit since you can code both things in the same language.
C# has many advantages over C++ and I personally use mostly C#, but I can clearly see many programmers who love C++.
Now going into your question regarding the similarities between C++ and C# the answer is yes and no. Yes in the sense that C#'s syntax is clearly derived from C++. Many things like ifs and for loops are written exactly the same, so if you know how to write an if in C++ you can write it in C#.
The difference (and a critical one that is) lies in the way the languages work. C++ is an strictly compiled language (it goes from C++ code to machine code). C# is an interpreted language (it goes from c# to MSIL and during runtime to machine code). In C# you can't use pointer arithmetic without explicitly allowing, in C++ you can (and will) use pointer arithmetic. C# has garbage collection, C++ does not.
In the end, as I said in the first paragraph you can use both languages to build an application, but it would be highly complicated. My advise to you is to learn a bit of C# and then decide which language you would prefer to build your GUI application. But don't believe even for a second that C++ can't be used to build a front-end since there are a myriad of frameworks for that. One I remember from the top of my head is Qt.
Another option for you is to use "C++/CLI" which is a flavor of C++ which can use the .NET Framework (the same framework C# uses)
EDIT: Thanks Jerry for pointing out that Managed C++ is obsolete and that C++/CLI is the one!

C# has braces, semicolons, and uses the concept of classes. It has "C derived" syntax, but otherwise is very dissimilar to C++. Java is really the precursor to C#, not C++.
You can build application GUIs using C#, and then use various methods of calling into C++ (such as P/Invoke). Unless you are using lots of existing libraries, or looking for absolute performance, its going to be a headache.
If you are looking for examples of modern Windows GUIs using C++, take a look at the Hilo example program.

It is not very difficult to switch to a new language. The few keywords you would have to learn are not the issue. What costs most energy if to get used to the new environment and class libraries. That is probably what you mean and it is true, you'll need some time.
Now coming to the split GUI in C# and code in C++, then you'll have to make all bindings and marshalling of parameters if there are buffers and strings for example. I don't think this would make your life any easier. Interfacing with native Dlls can become some pain. However if you use third party dlls and have already a large working codebase you could try to compile the logic code with /clr enabled. This generates a DLL that can be used from within .NET directly.
NOTE: WinForms is now out-of-date for new applications, consider using WPF instead. It scales nicely, but the learning curve might be steep for newcomers.

Please note that you have native C++ and C++/CLI, the first one is the one you have learned, but the second one is the one you will need to use if you want to combine it with a C# GUI. However, I would suggest you to stay away from C++/CLI because this will cause a lot of confusion if you don't have a solid ground in C++, C# and .NET.
The reason that you can't use the native C++ is because C# is a managed language, so you will either have to find another GUI that fits with C++ or you will have to go C# for everything. For more information about managed see the environment part of Difference between C++ and C#, the article will also provide you with a good comparison between both.

Well, this aint a direct answer but hope it will help you. Since you stated that, you are just started and you want C++ combined with GUI, I suggest you to take a look at Qt. IMO I found C++ and GUI made easy in Qt. Also it's good too.

Although it's not a direct response to the question you're asking, I'd first caution that WinForms are already basically a dead-end, so for new code you'd be much better off avoiding them. If you're going to do a GUI in .NET, the currently preferred choice is WPF.
Some people find C# an easier way to do a GUI. It's definitely true that Microsoft provides considerably more in the way of Wizards and such to do it with little or no coding if you use .NET for the job. Other people (especially those with more experience doing so) can produce a GUI in C++ just quickly (or even a little more so) using C++ instead.
Mixing languages like this can work well in relatively large projects where you have completely separate teams of people working on the different parts. For smaller projects where the same people typically work on both parts, the difference in syntax is at just about the worst possible level -- not enough different to really shift gears and think differently, but still enough different that you can't plan on just typing things and having any hope of them compiling. All in all, you're usually a lot better off picking one language and sticking to it.

What features should Java 7 onwards have to encourage switching from C#? [closed]

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Closed 11 years ago.
C# has a good momentum at the moment. What are the features that you would need to have in order to switch (or return) to Java?
It would also be quite useful if people posted workarounds for these for the current Java versions, e.g. Nullables being wrapped around custom classes, to make this a much more interesting wiki.

As a .NET/C# developer here are the missing features that annoy me. This list in no particular order - just as thoughts come to mind:
The Java library is too small. For common things I have to choose between 5 competing open source products because the base library is lacking in so many ways.
This is an Object Oriented programming language right? Why in the heck do primitive types not inherit from "object"?
Pointers
Lambdas
Closures
Partial Classes and to a lesser extent partial Methods
Real support for Generics
Using statements and Dispose - this was a real WTF for me. You really have to explicitly close connections in try/catch blocks. Poor Java guys!
Yield return would be nice
Unsigned integers - again WTF? I have to use number types larger than I need for what purpose again?
In Java you can return from final blocks of try/catch. A co-worker confused the hell out of me for hours by introducing a bug this way. This behavior should be prohibited as in C#.
I rarely have to use Java and when I do, I have all sorts of WTF moments.
Edit: I Removed for-each comment based on the fact it is no longer a missing Java feature since 1.5.

In my experience, Java vs. .Net is more of a business decision than a technical one. Shops with MS experience trend towards .Net and shops with Java experience trend towards Java & OSS. I've seen little evidence of people switching based upon language features. On the other hand, I've seen shops heavily tilt towards one platform b/c of one or two key employees they wanted to hire being knowledgeable in that area.

in no particular order:
function pointers (delegates); the whole passing interfaces around thing is stupid
real generics; what's the point of having type safe generics if the compiler can't even hold the meta data through a unit's compilation?
ui speed; all the self-drawing ui libraries are very slow compared to native controls wrapped in "managed" libraries, not to mention that microsoft's self-drawn ui is hardware accelerated through direct3d
an yield return construct; c# is so user friendly in this it's crazy
operator overloading
linq; just cuz its so addicting
properties; more synctatic sugar you get addicted to
better interop with native code; c#'s p/invoke and native com support makes interop so easy compared to jni -.-
first class value types; this goes hand in hand with real generics, having generic lists that never box/unbox in c# is part of why c# is faster than java.
and i'd say this is the most important one:
a responsive, informative debugger; nothing can even come close to visual studio right now

Just going off the cuff, I think the biggest thing Java 7 needs that everyone is lamenting the lack of is closures.

I'm a C# programmer and about one year ago I had to participate in the development of an application in Java. What I missed the most was:
Visual Studio (Eclipse is nice, but
VS is VS, especially Team Edition)
Comparing strings with ==
Properties
Basic types as first-class objects
(e.g. not "int" type vs "Integer"
class)
Anonymous methods (a workaround can
be made by using anonymous classes
but it is not the same)
LINQ
And there was one single Java feature that I missed when I went back to C#: explicit exception declaration in method signatures.
DISCLAIMER: I am speaking about a somewhat old project, I don't know if some of these features are present in current versions of Java.

Less heinous XML parsing and manipulation tools. Doing anything with XML in Java sucks.

I'll also give one answer the other way around. C# needs an enumeration implementation like Java has. Java's enumerations rock!
Let me add anonymous overrides to this list also. Sorry to go off topic, but C# needs the ability to anonymously override methods. I have been switching back and forth between Java and C#, and I have to say for unit testing legacy code, there is nothing better than anonymous class overriding.

I would need function pointers of some sort. The ability to use delegates in C# is so useful. There are so many times in Java where I want to create a map of delegates or function pointers as the solution, but I can't. I know you can simulate a similar thing in Java, but having the abstraction as part of the language is a huge plus!

Momentum. I have done a lot of development on both platforms. I'm enjoying the .NET side more because of the way the C# language is evolving. Java's evolution seems to be more a reaction to C# than an actual vision. So I think the best thing for Java to do is ignore .NET and create something new of its own.

Another one I would like is some equivalent to LINQ. I noticed how much I actually depend on the ability to use LINQ when I tried to do a top coder competition and realized they only support .NET 2.0. Once you get used to using LINQ to solve problem and make it part of your regular programming vocabulary it is very difficult to not see problems in that light. It is akin to using generics and then not being able to use generic.

I think, choice between Java and C# is not a question of language features, but a question of platform and ecosystem choice.
So, I doubt that any new syntactic sugar in Java or C# can lead to a significant amount of switchers between the platforms.
After all, JVM world has Scala and many language-sensitive developers are using it in some way.

I think, you should consider swithcing this holywar from "Java vs C#" to "JVM vs CLR", because JVM is (in the last years — mostly) not only Java, but also Scala, Groovy, Clojure, JRuby, Jython, and dozen of JVM-languages.

Properties!
Anonymous objects are nice too

Continuations, like Scala (on top of the rest) would be good too, for agents development.

Support to run over CLR (and vice versa perhaps for JVM) without IKVM and other such layers.

Let's be clear that we need to distinguish between Java and the JVM. I actually switched from C# to Java, but I admit it was not because of Java's amazing language features! In my very humble opinion, C# is the better language, and CLR is the perhaps a more elegant VM. However, even with Mono, you're not writing applications that run everywhere!
I think the greatest argument for Java is the amazing community it has. This is where the cutting edge technology is being developed, not at Sun (now Oracle). The Java community has consistently been the leader in developing Enterprise technologies. For instance, how long did it take Microsoft to provide a DI Framework? Where's AOP in .NET? When I start a .NET project, my foundation is Spring.NET, a Java port. When I need ORM, it's NHibernate. Need a testing framework? NUnit. I realize there are other OSS projects for the .NET platform, but their numbers and support from Microsoft are laughable compared to the Java community.

on the other side, has .net got enterprise open projects like Terracotta (semi commerical), Infinispan, Compass ? no. ncache (commerical), lucene.net are far behind them. Especially Terracotta is unique, it can improve some of your app x100, it's simply perfect and free (partitioning is commerical). If we implement a high load app in both .net with anything and java with terracotta + hibernate + terracotta-hibernate-integration, java app will probably far more performant than .net one. Ther're some ports to .net like nhibernate, log4net, lucene.net, but all of them are trying to catch java versions. And entity framework is a disaster, they have to start with nhibernate as the base or get some lessons from them.
.net is only working on windows (mono is far from enterprise, there isn't any enterprises using it), how much money does myspace.com spent for their 4000 windows web server licences ? 1 million ?
You can't install a simple plugin to VS (and can't do some other things) if don't buy professional edition,
Some windows instance types in amazon web services are nearly x2 price of the linux ones.
if you look at ohloh.net open source java project counts (with language comparison tools), you'll see that java has x5 more volume than c#.
also Java has %20 share on worldwide while c# has %4.x (source:tiobe.com)
Look at the top web sites; only microsoft and myspace are using .net. google, amazon, ebay, linkedin, alibaba, twitter (switched to scala from rails)... many of them are using java and many others are using php, ruby (facebook, yahoo,..)
As a language Java is far behind c#, but Scala (runs on jvm) is as good as c# and it's performance is nearly same as java and also it can use all jdk and other java code as his library.
I'm not saying java is better, but I'm saying java is as valuable as .net, too.

A native 'decimal' type for Java replacing the BigDecimal class would be nice. But Java thread-safe collections are nice.
Perhaps the question is not so much what Java 7 needs to persuade developers to use it, but more a case of what makes developers want to move from Enterprise/server-side java language to a different C# desktop Windows-only oriented world?
For most developers, the language isn't difficult to pick up be it Java or C#. I develop in Java, but Linq didn't take long to understand and use.
I think the choice of Java or C# depends on what motivates you personally -perhaps money? in which case either language will do whether they have certain features or not.
Ste

They should start by fixing the Calendar/Date related classes, even that seems too much to ask.

A simple way to map values in your model to the UI (like bind in Java/FX)

I think it depends on bussiness decisions, not the languages themselves.
But I really really really love C# lambdas and curry :D :D
http://mikeomatic.net/?p=82

a map({codeblock}) which runs over anything iterable would be nice. And filter too. And being able to return multiple values easily from a method.
(a,b,c) = getThreeValues();
(would assign the individual variables a, b and c).
Actually I just think they should have Haskell as a supported scripting language on the JVM :D

linq, lambda, anonymous types

I don't see any point in "luring" anyone anywhere. They solve different problems and you should use whichever one suits you.
Java has less "Language" and less structures to trip up new people, it's platform independent and it doesn't change too fast allowing old code to stick around for a LONG time (Good for some large companies).
C# has tight desktop integration and a slew of nice features that make it more fun to program. It has .net integration. It has pointers, closures, etc which make it harder for n00bs (a valid language target, hence Basic) but more fun for experienced programmers--I haven't convinced myself that these features make you more productive, but in some situations they can make your code a lot nicer! Also if you need pointers, you need pointers.
I don't see a whole lot of overlap in target audiences. Why change a language to attract programmers when it's healthier for the entire industry to have two healthy languages each targeted at solving different problems attracting different developers?

Migrating a project from C# to Java

With some changes in the staffing at the office, the levels of C# expertise has dropped off precipitously and there are now more Java developers. It has gotten to the point where the higher-ups are considering moving an existing .NET project written in C# into the Java world.
Aside from the obvious problem of starting completely from scratch what are the possible ways that this company can accomplish a successful move of development on a project from .NET C# into Java?

Here are things to consider:
Is this big project? If Yes, try to stick with C#
Is this medium sized project with components? If No, try to stick with C#
Is this small project meant to be deployed on windows only? If yes, try to stick with C#
Is this old source code? If Yes, try to stick with C#
Do you use windows OS specific APIs? If Yes, try to stick with C#
Do you use any third party APIs without Java counterpart? If Yes, try to stick with C#
Do you use .Net in "deep"(data binding, User controls etc.)? If yes, try to stick with C#
Migration time is more acceptable than getting new/converted C# guys? If no, try to stick with C#
Do you think end users will not be receptive of changes, if you are to use Java framework which will change presentation? If yes, try to stick with C#
Check commercials
If you decide to convert:
Go per component
Go per layer
Have lots of tests
Check if there are tools to help (however small help may be) with migration

Just to add to Brian and Eric's opinions, I would say that picking up C# for a Java developer should be straightforward in my opinion. They are conceptually very similar languages and I would suggest training your Java developers to gain some C# skills so you won't be forced to go to the hassle of a migration process.

I subscribe to Joel's view that a total rewrite is almost always a mistake. Other posters are right: C# and Java are similar enough that any competent Java developer should be able to become competent in C# in a matter of weeks or months. That's not to say they will be experts. That takes longer but as long as you have some C# developers who can guide the process then you should be OK.
It's hard to comment on whether or not such a transition is a good or bad idea without knowing specifics of your application: size, type of application, industry and so on.
I would be extremely reticent about such a switch because, in my humble opinion, C# is now a much more modern language than Java and I say this to you as someone who has been a Java developer ofr over a decade (since the 1.0.2/1.1 days).
That's not to say that Java is bad. It's not. Sun does have a cloud hanging over it and demonstrated an unwillingness or inability to drive the platform forward in recent years.

Regardless of the languages involved, the management of this company sounds insane. For anything other than a trivial application, how can it be economically sensible to rewrite an entire code base from scratch instead of just hiring a single person with some skills in the right language? Is this a business with that well-known problem: too much spare cash?!
How long has the existing code been in development? If it's barely started, I could understand this. If it's seen a release and has active users, it will never make sense to throw it away. If you donated the C# code to a start-up with the right skills, think how much of a head start they would have over you.

Before you finish converting the .NET project into Java, all those Java developers who were part of the conversion project will have learned C#. So then you don't anymore need to convert it to Java (and you can throw away all Java code which was produced in the conversion), because now you have a development team which can do both Java and C#. Problem solved. :D

Have a look at Net2Java, which puports to assist in converting your code from C# to Java. I doubt it'll be perfect, but its one way to remove a lot of drudgery from the task, leaving you with the kinks of incompatible framework calls and language features to iron out.
Once you've done that, your task is like any other large migration project - test, test and test again. Unit tests, System integration tests, then end-user tests. You should havew those tests already in place that you used with the original application, apart from the unit tests, they will still be relevant.

If there are any components that are already isolated or any of it uses a service-oriented architecture, you could conceivably migrate one component at a time (where each individual component is a rewrite) and still have the components talk to one another using the same interoperable network protocols. Probably depends on what type of app we're talking about.

Make sure you have tons of tests, because such a migration will bite you where you expect it least.

Do you have more .Net or more Java applications in production. If your already have a substantial investment in .Net servers and applications, why not ask for volunteers among the Java developers to move to .Net? The language and syntax is very similar, so the hard part would be learning the framework and unless they would spend all their time doing UI development even learning the framework is not that hard.
In our office we have a number of very good developers who move back and forth between Java and .Net as needed.

I am not a Java expert, but from my experience working with Java code whilst being a C# fan, the following are some of the possible headaches:
Generics are implemented differently in Java and C#.
Boxing/Unboxing behaviors are different between Java and C#
Java class naming convention + lots C# generated code
String handling (i.e. Unicode/ASCII concerns) can be problematic depending on the quality of Java/C# code being ported over.
Personally, I don't think writing from scratch is a bad idea at all. Since you already have a working architecture.

In order to prove to management, you always needs to talk in terms of ROI and numbers. Show them that if you move these applications, it will take tremendous amount of time, QA resources, and can easily take a back seat if it gets de-prioritized due to some other project or new development taking importance.
I had success when I showed them the timelines, ROI, work involved, money involved, etc.
So now coming to the actual point, I do think Java developers would be able to support C# unless they have some fundamental mental block against Microsoft technolgies.

Possibly you could use jni4net - opensource bridge ?
Or list of other options I know.

I'm somewhat surprised noone even suggested the idea of rejecting migration.
I do not believe a C# developer can be forced to switch to Java (or vice versa) because he was told to (well, if he's threatened with a gun then maybe). I takes much time, exercise and passion to master at least one technology stack. You just can't start overnight with a new technology and expect to provide the same quality.
I'd personally not bother until told to start migration. At which point I'd tell the manager that I'm .NET guy and won't switch to another technology just because they decided to.
As for the technical side, it's not the language syntax that differs but rather libraries and their features. Of course, if all the latest bells and whistles of .NET 3.5 have been extensively in use then the language difference will provide you with a real challenge.
That's certainly a funny way, just decide to migrate applications from .NET to Java. Someone has no idea of the hassle involved...

I realize that this is an old question but to anyone else going down this path, you could try this open source C# to Java Converter:
http://www.cs2j.com/

Why should I learn C#? [closed]

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I want to know why I should learn C#?
What features does C# have that Java does not?

C# is an object-oriented high-level language which can be useful to develop applications.
It supports getter/setter constructs, delegates and true generics, which Java does not.
C# usually feels more "native" on Windows, since Windows.Forms and WPF are closer to native code than Swing.
However, Java is more cross-platform than C#(even though project "Mono" is changing that)

There's a whole lot of differences: http://en.wikipedia.org/wiki/Comparison_of_C_Sharp_and_Java
Whether you should use one over the other depends on your priorities. What do you want to write in them?

C# (and other the CLR languages) have aspects of functional programming (such as delegates and closures) that make some types of development and design patterns easier. See this post by Steve Yegge for more. Delegates can make code much more expressive and concise.

You should learn both, and use each of them as appropriate. I don't feel like it's a "which one should I learn?" kind of question. (Or a "I know Java, why should I learn C#?" question.) That comparison that Welbog posted will help you decide when to use one over the other. But, myself, I like having both in my toolkit.

Syntax:
They are both reasonable languages--they support pretty much the same high level structures and designs (OO, encapsulation, ...) and are fairly equal up until you get down to the code level (which overall isn't that big a deal. C# beats java in features, Java beats C# in simplicity I guess).
Portability:
My biggest factor has been that lately I've worked on apps for a spectrum analyzer and upcoming cable systems. Neither would have been remotely programmable in C# (you are completely reliant on microsoft to port the runtime to your platform of interest. Java is open source (there may still be one or two little pieces that aren't, but they are sincerely working on that and it's enough that you can port it and use it just about anywhere.
If you are only ever interested in Windows and if you'd like to take advantage of tight, simple integration with windows, then C# is the platform for you.
VM
Both languages include a "Runtime" that can support other languages--and those other languages generally have access to the (very rich) libraries provided in each environment.
Microsoft can run a few (a dozen) languages on it's VM, none as impressive as C# (although Ruby and Python could be good--are they fully available yet)?
The JVM has a few hundred including some cutting-edge experimental languages that often run as well as or better than their native counterparts. Some are considered the next generation in programming, as different from Java/C# as they were from C. I looked into Scala, but I must be getting old, it just hurt my head, but I admit there are some very advanced concepts available in there. Groovy rocks.
System integration/tools:
C# wins hands down since Java can't commit to any one platform. C# is also very well integrated with databases and other external dependencies, Java is getting better integrated, but the tools are a little more mismatched. C# the entire toolset tends to be very integrated since it all tends to come from a single vendor.
Number of platforms using it (number of potential customers):
Last I heard, Java wins hands down. WAY down. Every try to figure out how many phones, microwaves, TVs and toasters might be running Java? The number dwarfs every other language combined as I understand it...

the only reason you should is because you want to
C# is a
multi-paradigm programming language that encompasses functional, imperative, generic, object-oriented (class-based), and component-oriented programming disciplines
so you get to learn a lot of tricks from different paradigms, all in a single language

There are lots of questions that people have asked on this topic already. Read up, they've got good infos there. :)

The biggest reason, imho, why is because (for windows desktop apps at least) Java UI is godawful ugly. Fugly ugly. Vomitously ugly. Ugly like the kid you'd have if you impregnated your sister.
If you are required to run on any OS, Java is your best option (tho Mono is catching up!). But if you're programming for the Windows environment, C# is a dream to code and looks like any other native application.
Other than that, I'd say Linq. And the ability to fail fast on exceptions rather than having to handle exceptions everywhere (like we actually know how to handle each and every exception). Oh, and Linq again. Linq is so beautiful... to me... Can't you see?
Crap, forgot about lambdas. Damn, I love lambdas and all their closure goodness.

Simple answer -- C# is the primary language for developing Micorosft applications at this point. Learning it opens up a new world of potential opportunities to work on Microsoft-based applications.
Also, it's not really that hard to learn. Just a little harder than VB was, but with lots of OO power.
Some people would say C# is Microsoft's Java -- actually they look almost identical, just minor differences but different class libraries. If you already know Java, picking up C# shouldn't be too hard.

I can't believe nobody has posted this yet..
Because, it is a fun language. Personally I think Java is a rather nasty language (still can be fun), but not as enjoyable as C#.

Do you need to learn C#?
Is your job situation going to improve?
Do you want to learn something new?
Is the development environment better in C#, is the tooling better?
Do you think you can do something in C#, that you can't do in Java?
Maybe a generic language for desktop, web and mobile - but Java has this as well.
Just a few questions you could use to decide.
I'm C# myself, started out in Java when I was introduced to programming. I think Java did a fantastic job for me in understanding programming, mostly because there were no magic IntelliSense, or form designer for Windows apps - we had to write the whole damn thing our selves. Which was good, when you're learning. But I think C# and the whole .NET/Visual Studio eco-system enables you to be more productive.

More important than the feature of the language are the run-time environment and the libraries.
C# and Java have a different set of libraries, frameworks, operating system interactions, etc.

Based on the question seems like you are not interested in learning it for the sake of knowing more about programming and clearly looking for practical reasons.
That is why I don't think you should bother learning it, since it will be just another tool to accomplish same thing in your toolbox.

I like what Welbog wrote. I would add that it would also depend on where you're at professionally, your interests, and your job prospects /interests.
If you're you've just started to learn Java, then picking up a little C# might help in terms of broadening your programming horizons. The languages are similar (roughly speaking), but of course there are nuances to say the least in programming in one versus another. If you've been programming Java for awhile, then perhaps you'd be better off either expanding your J2EE area of expertise or maybe looking at other supporting areas and/or languages.
In terms of job prospects, you might find companies in your area hire more .NET developers than Java, or vice-versa. You might also want to look at companies you want to work for and make sure your skill set matches. For example, if you've dreamed at working at a particular firm who uses JSP, just as an example, then sticking with Java would be better.

It is not C# that you should want to learn but .NET Framework and related technologies.
Think rather J2EE vs .NET.
Why would you want to learn .NET? It's up to you to decide. Like Java it's one of the few major development platforms. It is functional, very actively developed and supported with a huge community knowledge base.

To me the choice is as simple as I need to use .NET libraries, so I'll use C# or I need to use Java libraries so I'll use Java. If I'm working on something on a Windows client I'll use C#, if I'm working on something that needs to run against the P6 Integration API I'll use Java.
You shouldn't feel like you you are missing something or should use one or the other. Look at what you have to do and pick the best tool for doing that.
It's tough to list on a post here all the features of the .NET Framework, just like it would be tough to list all the features contained in the Java SDK Libraries.

Learning C# because it may or may not have features that Java doesn't have seems like a very odd reason in opinion (it does have a number of features, that Java doesn't but so does F#, LISP, Haskel, Ruby, Lua and even COBOL).
You should learn C# because
You need to (to keep or get a job, stay in school, whatever)
You want to
It is fun to expand your horizon
Any or all of the above

There are some syntactic sugar advantages in .NET such as LINQ or Properties. (Yes, you don't have properties - not to mention auto-properties - in Java).

Strategically, it helps to know several languages as demonstrated by a little research. Currently, PHP, Java, and ASP.NET (C#) are the most widely used server-side programming technologies (see https://w3techs.com/technologies/overview/programming_language/all). Therefore, knowing all three empowers your backend engineering potential.