What are the differences between Generics in C# and Java... and Templates in C++?

I mostly use Java and generics are relatively new. I keep reading that Java made the wrong decision or that .NET has better implementations etc. etc.

So, what are the main differences between C++, C#, Java in generics? Pros/cons of each?

Wikipedia has great write-ups comparing both [Java/C# generics][1] and [Java generics/C++][2] templates. The [main article on Generics][3] seems a bit cluttered but it does have some good info in it.


[1]:

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[2]:

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[3]:

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Anders Hejlsberg himself described the differences here "[Generics in C#, Java, and C++][1]".


[1]:

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The biggest complaint is type erasure. In that, generics are not enforced at runtime. [Here's a link to some Sun docs on the subject][1].

> Generics are implemented by type
> erasure: generic type information is
> present only at compile time, after
> which it is erased by the compiler.


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C++ templates are actually much more powerful than their C# and Java counterparts as they are evaluated at compile time and support specialization. This allows for Template Meta-Programming and makes the C++ compiler equivalent to a Turing machine (i.e. during the compilation process you can compute anything that is computable with a Turing machine).

In Java, generics are compiler level only, so you get:

a = new ArrayList<String>()
a.getClass() => ArrayList

Note that the type of 'a' is an array list, not a list of strings. So the type of a list of bananas would equal() a list of monkeys.

So to speak.