Incompatible types with generics problem

Question

Hi,
I get a mysterious compiler error:
C:\Documents and Settings\Eigenaar\Mijn documenten\NetBeansProjects\Tests\src\tests\genericstest.java:26: incompatible types
found : tests.Store<T>
required: tests.Store<T>
return store;
1 error
BUILD FAILED (total time: 0 seconds)
in the following code:
class Supply<T extends Supply<T>>{}
class Store<T extends Supply<T>>{ }
class A<T extends Supply<T>>{
    private Store<T> store;
    class B<T extends Supply<T>> {
        public Store<T> getStore(){
            return store;                         <-- compiler error!
}Any help would be greatly appreciated.
Edited by: farcat on Jan 13, 2009 1:23 PM

Answer 1

Note that the type parameter T used to define class B is not the T used to define class A. What you wrote can be more clearly written:
class Supply<T extends Supply<T>>{}
class Store<T extends Supply<T>>{ }
class A<T extends Supply<T>>{
    private Store<T> store;
    class B<U extends Supply<U>> {
        public Store<U> getStore(){
            return store;
}Which produces the more readable error message:
A.java:10: incompatible types
found   : Store<T>
required: Store<U>
            return store;B, being a nested, non-static class is already parameterized by T:
class Supply<T extends Supply<T>>{}
class Store<T extends Supply<T>>{ }
class A<T extends Supply<T>>{
    private Store<T> store;
    class B {
        public Store<T> getStore(){
            return store;
}