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Hejlsberg Talk About Generics in C# and Java
An anonymous reader writes "artima.com has a very interesting interview with Anders Hejlsberg - the Borland guy now at Microsoft who can best be defined as MR C# - doing all the stuff that Borland wouldn't let him do. He discusses generics in C#, Java (1.5) and C++. Naturally there is the chance of bias but he does raise some interesting points againt Java's generics. Specifically that Java's genericised collections will have to box all primitive types as full objects, whereas C# does not. This is a big performance plus for C#. Java created the primitive types in the first place to address performance concerns but appears to be stepping sideways here. I can't help wondering if Sun has taken this approach to get the syntatic sugar in the language without requiring a bytecode change, but perhaps in a future VM version will allow primitive generics (obvioulsy forcing a bytecode regeneration)?"
Just read a little further into the article. It seems that to avoid having to make changes in the VM, the Java generics have to become just like the current containers at the bytecode level. The main difference would be taht instead of having to type all the ugly type casts yourself, the compiler would do it for you. Obviously, this doesn't lead to any performance increases over Java 1.4 containters.
Compare this to, let's say, C++ templates, where the compiler makes a new copy of the template class specifically for each and every type you use on it. That makes the executable size increase a bunch, but it allows the compiler to pay the performance price, making the code perform almost like a program where a human programmer would have written a copy of the template class for each and every type you ever used it with.
Since the design of the java 1.5 generics is public knowledge, it's pretty easy for anyone with a reasonable programming knowledge to analyze it. It just seems that run-time efficiency wasn't the first thing in the designers minds.