1. The overall architecture (with the JVM) made it slower than the equivalent C# code.
2. C# really started embracing modern language features at a time when Java was kind of languishing (lambda functions, async patterns). Java seems like it's been in perpetual catch-up since then.
(Not OP, disclaimer, I work for Microsoft and this is only my opinion).
> I haven't kept aware of changes to Java in the last decade, but the things I didn't like about it then were:
It's almost a shame. I am genuinely impressed with the gains the team has made in both, language aspects as well as JVM technology. They have some brilliant people working on it and I love to hear their talks (Brian Goetz and Mark Reinhold, mostly).
But I suppose I would say the same about .Net, it's just that you guys have much less public exposure of your internal reasoning.
Spring is a de-facto extension of the core java libraries and alternatives like Quarkus follow the same mental model with a better technological foundation.
I could continue to point hundreds of technical differences but that's the trees and not the forest.
Have you never written a plugin or a mod?
Yes, AOT and cross-compilation are very good nowadays. This only replaces one of bytecode's features.
As soon as you AOT compile CLR or JVM languages, you lose access to the stable, feature-complete ABI that bytecode provides. Heck, many languages built from the ground up for static compilation like Go and Rust still have dismal ABI stories. The only exception I can think of is Swift, and it didn't come by it easily. AOT also imposes limits on reflection and runtime codegen (often, to the point of totally removing them).
If your software exists only in a walled garden, only gets deployed to infrastructure you 100% control, can't be extended at all, and/or can only be extended by full recompilation, then bytecode may seem useless. But that isn't the whole world of software.
I think the progress on Java and the JVM has been nothing but impressive. Not only compared to the baseline to where things were 10/15 years ago, but simply how much stuff comes out each year and how well-thought it all is.
Frankly, it's an inspiration for my private and professional projects.
Java is fast and reasonably safe. It has a lot of software (especially OSS) software. Its package system (Maven and the like) is ok, but not great. The language occasionally gets new features, but change is slow.
To a first approximation, C# is a lot like Java, so it is relatively easy to switch. But C# is, hands down, a better language. The most obvious thing that a developer might notice that that C# does not force you to be extremely verbose like Java, although you can code in the Java style if you like.
Having switched my course from Java to C#, the most obvious "win" was the fact that, every lecture, I would delete some slides that explained painful Java corner cases to students. For example, Java's implementation of generics. Boxed types are necessary, and explaining them to students who have never seen any form of polymorphism before is difficult. After an entire semester of deleting a handful of slides each lecture, I have save _three entire lectures_ worth of corner cases!
Some C# niceties:
* Everything is an object, even value types! So our favorite `ToString` and `GetHashCode` methods, etc, are all there. * Generics work as you would expect with very few weird corner cases. No boxed types because... everything is an object! * The last two facts mean that you also get generic arrays, which are fantastic (and, incidentally, are also _implemented_ in C#, which is super cool). * By default, reference types are not nullable. This is a little bit of a pain for an intro data structures course (we turn them off), but it is a great idea for commercial programming. * switch statements work the way you would expect a modern switch to work, and in some cases they even do exhaustiveness checking like a functional language. * Speaking of... LINQ! * In general, the standard library is also better organized. Interfaces start with "I". Collections libraries have been carefully designed and learned many lessons from Java. A good example of an improvement over Java is the IEnumerable<T>/IEnumerator<T> class, which is simpler than Java's Iterator<T>. * Type inference is limited compared to a functional language, but it is dramatically better than Java. Being able to write `var` is wonderful. * Properties are really nice, and the shorthand syntax for property getters/setters saves a lot of time. * C# has a rich set of value types, including structs. Java may have added something like this, since I remember the Scala people hacking away on it, but it is used pervasively in C#, and you can make very fast data structures that take advantage of spatial locality. Rolling one's own hash table implementation in C# is actually kind of fun. * .NET's runtime reflection capabilities are amazing. All of my autograders make extensive use of reflection instead of forcing students to compile with interfaces; this gives them a degree of freedom in implementing things. * NuGet is a million times easier to use than Maven.
The downside is that C# is definitely not as fast as Java, in particular when the runtime is starting up. I remember how painful Java startup used to be, so I am optimistic that this will improve eventually.
Anecdotally, my students this semester are demonstrably more capable programmers after a semester of C# than a semester of Java. It might just be that I got lucky with this group, but I have been teaching this same course (except in Java) for the last 7 years, and this feels like a real effect.
Took me a moment to realize you meant that 'Java has corner cases because everything is an object' but yes.
Will also add the 'advantage' that for value types (i.e. struct) the generics are 'specialized' for the type, in certain cases you can use that for performance optimizations. (although it can have downsides.)
> The last two facts mean that you also get generic arrays, which are fantastic (and, incidentally, are also _implemented_ in C#, which is super cool)
And, fun side note, the generic arrays actually existed before real generics (and we get fun hacks in the VM as a result!)
.NET does still have funkiness around Array Covariance tho, which sometimes can be a pain.
> By default, reference types are not nullable.
This is a newer feature and great, however it requires people to (1) use libraries that properly do it and (2) requires you to have the right tag in the csproj to flag the NRT warnings as errors. I've yet to see a shop that has adopted (2) as a default.
> In general, the standard library is also better organized. Interfaces start with "I". Collections libraries have been carefully designed and learned many lessons from Java. A good example of an improvement over Java is the IEnumerable<T>/IEnumerator<T> class, which is simpler than Java's Iterator<T>
Yes and also the sugar around yield syntax to do generators.
> Properties are really nice, and the shorthand syntax for property getters/setters saves a lot of time.
I still remember getting called into a Dev Manager's office, he's a JVM guy and he's goes into this overview of Lombok and how the JVM folks want to use it and he asks what I think and I'm like "Gee wow give me a moment I thought Java had AutoProps by now". (I think it was the first time he was impressed with C# as a language lmao, He and later I were disappointed in .NET's lack of a good set of thread pool abstractions...)
> .NET's runtime reflection capabilities are amazing. All of my autograders make extensive use of reflection instead of forcing students to compile with interfaces; this gives them a degree of freedom in implementing things.
That is so freaking cool and I love it. Profs like you made college fun back in the day.
> NuGet is a million times easier to use than Maven.
Truth; every time I have to do a thing in JVM dealing with maven feels like I need a goat or chicken to make anything work right.
> The downside is that C# is definitely not as fast as Java, in particular when the runtime is starting up. I remember how painful Java startup used to be, so I am optimistic that this will improve eventually.
We have AOT and R2R nowadays, I'm not sure if it's 'JVM Fast' for something like a webservice but unless you're pulling in something like an ORM it's typically fast enough I can't observe a difference as a user for utility apps/etc... Curious what examples you have in mind?
Don't get me wrong, there are some features like "abstract static" in interfaces which give C# superpowers... until you realize that this only works one layer deep. Or the non-break switch expressions, which require a return type. Lack of an equivalent to Java's "Sealed Classes" (that you can switch over). Or that you can't validate primary constructors up until recently.
Lack of value objects are definitely hurting, but JEP401 addresses this and is available as preview as of now. I am absolutely blown away by the depth of their value-narrative and I think they uncovered something much deeper than "value or not" with gradual performance gains based on gradual constraints.
But I absolutely see the value of C# in teaching. Java works more via libraries and convention, whereas C# has ingrained many concepts directly into the syntax level.
But maybe I am a Java fanboy, haha. I even prefer the Erasure of Generics, the times it has complicated my code in C# is much higher by now than I ever thought it would be.
Does Java have real generics yet?