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Re: Generics and downcasts

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On 25.04.17 22.20, Arne Vajhøj wrote:
> .NET got generics relative early in its history, so MS decided
> that compatibility with old collection classes was not that important.
> Java was in a different situation, so type erasure and collection
> compatibility was chosen. And we have to live with it.

The bad news is that although this breaking change they did not manage 
to give their new container classes a consistent interface. There are at 
least 4 distinct and fully equivalent implementation of the Count 
property. And methods with the same name (like Add) have significantly 
different semantics in different container types.

>> There are other pitfalls that are by far more expensive.
>> E.g. if you miss to declare a trivial Java method as final. This
>> prevents the JIT from inlining the method body. This may add an overhead
>> of an order of magnitude or even more.
>
> I think this is a myth.
>
> https://www.ibm.com/developerworks/library/j-jtp1029/  (Brian Goetz 2002)
>
> <quote>
> Like many myths about Java performance, the erroneous belief that
> declaring classes or methods as final results in better performance is
> widely held but rarely examined. The argument goes that declaring a
> method or class as final means that the compiler can inline method calls
> more aggressively, because it knows that at run time this is definitely
> the version of the method that's going to be called. But this is simply
> not true. Just because class X is compiled against final class Y doesn't
> mean that the same version of class Y will be loaded at run time. So the
> compiler cannot inline such cross-class method calls safely, final or
> not. Only if a method is private can the compiler inline it freely, and
> in that case, the final keyword would be redundant.
> </quote>

I never said that the Java compiler might inline such function calls. 
This is up to the JIT.


Marcel

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Re: Generics and downcasts Marcel Mueller <news.5.maazl@spamgourmet.org> - 2017-04-25 22:07 +0200
  Re: Generics and downcasts Arne Vajhøj <arne@vajhoej.dk> - 2017-04-25 16:20 -0400
    Re: Generics and downcasts Eric Douglas <e.d.programmer@gmail.com> - 2017-04-25 13:35 -0700
      Re: Generics and downcasts Arne Vajhøj <arne@vajhoej.dk> - 2017-04-25 19:54 -0400
    Re: Generics and downcasts Marcel Mueller <news.5.maazl@spamgourmet.org> - 2017-04-25 22:40 +0200
      Re: Generics and downcasts Eric Sosman <esosman@comcast-dot-net.invalid> - 2017-04-25 18:13 -0400
      Re: Generics and downcasts Arne Vajhøj <arne@vajhoej.dk> - 2017-04-25 19:53 -0400

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