Computer Science Canada Odd problem with generics in Java 1.7 |
| Author: | matt271 [ Mon Sep 17, 2012 11:32 am ] |
| Post subject: | Odd problem with generics in Java 1.7 |
Hi, I am having an odd problem with generics in Java 1.7. As I am not admin on this current computer, I cannot install 1.6 and test if it is a problem there too. Basically, I have some interface called MyInterface, and some class called MyClass that implements MyInterface. Then I have a method myMethod that takes a parameter of some generic instance of MyGenericClass<MyInterface> and I want to pass it an instance of MyGenericClass<MyClass> is this possible? The setup is like: public interface MyInterface; public class MyClass implements MyInterface; public class MyGenericClass<T>; public void myMethod(MyGenericClass<MyInterface> ditto); and the problem is I cannot state: myMethod(new MyGenericClass<MyClass>()); My question is why does this not work? Is this something you cannot do in java? Is something different in Java 1.7? I know I can say MyInterface bleh = new MyClass(); So what is the difference to putting an instance of MyClass into a generic method expecting a MyInterface? I think if this is not possible, it would not make sense to allow a generic type of an interface? Thank You |
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| Author: | DemonWasp [ Tue Sep 18, 2012 1:07 am ] |
| Post subject: | RE:Odd problem with generics in Java 1.7 |
In general, Parameterized<C> is not an instance-of (instanceof operator) Parameterized<I >, even when C implements I, or C extends I. The full explanation for the reason behind this behaviour is a little involved, and is explained here: http://docs.oracle.com/javase/tutorial/java/generics/subtyping.html |
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