Double generic constraint on class in Java: extends ConcreteClass & I

By : axk
Source: Stackoverflow.com
Question!

Is there a way to define a generic constraint in Java which would be analogous to the following C# generic constratint ?

class Class1<I,T> where I : Interface1, Class2 : I

I'm trying to do it like this:

class Class1<I extends Interface1, T extends I & Class2>

But the compiler complains about the "Class2" part: Type parameter cannot be followed by other bounds.

By : axk


Answers

The simplest way I can see of resolving the Java code is to make Class2 an interface.

You cannot constrain a type parameter to extends more than one class or type parameter. Further, you can't use super here.



This code compiles here fine:

interface Interface1 {}

class Class2 {}

class Class1<I extends Interface1, T extends Class2 & Interface1> {}

Why do you need the I type there when you assume only Interface1 anyway? (you won't know anything more in your class about I than it extends Interface1)

By : mitchnull


Even though not all parsers read the whole file into memory, if you really need a rule of thumb I would say not bigger than half of your available ram. Anything bigger will likely be way too slow :)

By : Sec


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By: admin