Is it possible to impose an upper bound (super X) on a named Generic type?
Suppose I have the following static method and interface (List is java.util.List). Note that the static method enforces a "super Foo" on the wildcard type of the list.
public class StaticMethod {
public static void doSomething(List<? super Foo> fooList) {
...
}
}
public interface MyInterface<T> {
public void aMethod(List<T> aList);
}
I would like to be able to add a class which implements the interface using the static method as follows:
public class MyClass<T> implements MyInterface<T> {
public void aMethod(List<T> aList) {
StaticMethod.doSomething(aList);
}
}
This obviously won't compile becaus开发者_运维问答e T does not have the "super Foo" constraint. However, I can't see any way of adding the "super Foo" constraint. For example - the following is not legal:
public class MyClass<T super Foo> implements MyInterface<T> {
public void aMethod(List<T> aList) {
StaticMethod.doSomething(aList);
}
}
Is there any way of solving this problem - ideally without altering StaticMethod
or MyInterface
?
I'm going out on a limb here, but I think lower bounding is the problem here, because you have to know about the actual class that fits the bound when you refer to it... you can't use inheritance.
Here's a usage that compiles, but notice that I need to name the actual class that is a super of Foo:
class SomeOtherClass
{
}
class Foo extends SomeOtherClass
{
}
class StaticMethod
{
public static <T> void doSomething(List<? super Foo> fooList)
{
}
}
interface MyInterface<T>
{
public void aMethod(List<T> aList);
}
class MySpecificClass implements MyInterface<SomeOtherClass>
{
public void aMethod(List<SomeOtherClass> aList)
{
StaticMethod.doSomething(aList);
}
}
Comments?
p.s. I like the question :)
If you are sure that aList
contains objects that can be safely cast to <? super Foo>
, then you can do:
public static class MyClass<T> implements MyInterface<T> {
@Override
public void aMethod(List<T> aList) {
StaticMethod.doSomething((List<? super Foo>) aList);
}
}
See the complete and working example: http://ideone.com/fvm67
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