Differences between MSIL and Java bytecode?

Question

I'm new to .Net and I'm trying to understand the basics first. What is the difference between MSIL and Java bytecode?

Answer 1

First off let me say that I don't think that the subtle differences between Java bytecode and MSIL is something that should bother a novice .NET developer. They both serve the same purpose of defining an abstract target machine which is a layer above the physical machine being used in the end.

MSIL and Java bytecode are very similar, in fact there is a tool called Grasshopper which translates MSIL to Java bytecode, I was part of the development team for Grasshopper so I can share a bit of my (faded) knowledge. Please note that I stopped working on this around when .NET framework 2.0 came out so some of these things may not be true any more (if so please leave a comment and I'll correct it).

• .NET allows user defined types that have value semantics as apposed to the regular reference semantics (struct).
• .NET supports unsigned types, this makes the instruction set a bit richer.
• Java includes the exception specification of methods in the bytecode. Although exception specification is usually only enforced by the compiler, it may be enforced by the JVM if a class loader other than the default one is used.
• .NET generics are expressed in IL while Java generics only use type erasure.
• .NET attributes have no equivalent in Java (is this still true?).
• .NET enums are not much more than wrappers around integer types while Java enums are pretty much fully fledged classes (thanks to Internet Friend for commenting).
• .NET has out and ref parameters.

There are other language differences but most of them are not expressed at the byte code level, for example if memory serves Java's non-static inner classes (which do not exist in .NET) are not a bytecode feature, the compiler generates an additional argument to the inner class's constructor and passes the outer object. The same is true for .NET lambda expressions.