问题
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.
回答1:
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.
回答2:
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)
来源：https://stackoverflow.com/questions/132353/double-generic-constraint-on-class-in-java-extends-concreteclass-i