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考虑下面的类:Java泛型,通配符,集合:编译错误
import java.util.ArrayList;
import java.util.Collection;
public class Main {
private static class A {
}
private static class B<T> {
private void thenReturn(T value) {
}
}
private static <T> B<T> when(T methodCall) {
return new B<T>();
}
private static Collection<? extends A> method() {
return new ArrayList<>();
}
public static void main(String[] args) {
Collection<? extends A> result = new ArrayList<>();
// Does not compile.
when(method()).thenReturn(result);
}
}
我得到的编译错误The method thenReturn(Collection<capture#1-of ? extends Main.A>) in the type Main.B<Collection<capture#1-of ? extends Main.A>> is not applicable for the arguments (Collection<capture#3-of ? extends Main.A>)
究竟我在main方法,以便它会编译改变?有没有比
更好的解决方案public static void main(String[] args) {
Collection result = new ArrayList<>();
when(method()).thenReturn(result);
}