java - Direct Generic Exceptions -

my question follow-up question:

why doesn't java allow generic subclasses of throwable?

the question answered perfectly, on indirect generic exception, that's:

public class myexception<t> extends exception { 

what left void, direct generics:

public static <t extends exception> void checkforexception(class<t> extype) {      try {         // code     } catch (t e) {         e.printstacktrace();     } } 

why not allowed?

though, reason think not allowed, t type, explicitly caught:

// if t ioexception catch(t e) { } catch(ioexception e) { } 

but reason block it? same effect, done without generics too:

catch(exception e) { } catch(ioexception e { } 

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here's documentation of above restriction.

because in java type variables, i.e. t, not reifiable due type erasure.

this means compiler not have t @ runtime @ all.

hence there no way catch block of yours ever know t was. , no, can't treat base type. different. if had

catch(t e) { } catch(mybaseexception e) { } catch(myapplicationexception e) { } 

and t extends mybaseexception. see how got bad quick?

read more in excellent java generics faqs - under hood of compiler

personally i've never liked type erasure, language designers swore had reasons using it. here are.