webMethods Knowlegebase : Cannot cast an array of interfaces to an array of objects (1778768)

Problem

The problem here has been found that we do not like casting a full array of a cross-compiled Java interface into an array of generic Java Objects.

We are casting an array of Java Action[] objects into Object[]. Although we can cast arrays of implementations, we cannot cast without exception when the Array type is of a Java interface. This is why making a new Object[] array and assigning each index to match with the Action[] array, with the types cast individually as Java Object works - because we are dealing with specific implementations in each case. Similarly, an array of an implementation of Action (e.g. DefaultAction?[]) would cast fine to Object[] however casting an array of Java interfaces to Object[] will cause the C# system to throw a ClassCastException, presumably because the interface itself does not explicitly extend Java Object and thus cannot be cast.

Example code:

Java:

public interface Thing {

}

public class DefaultThing implements Thing {

}

C# referencing the cross compiled Java:

Thing[] collection = new Thing[] { new DefaultThing(), new DefaultThing() };

DefaultThing[] collectionImpl = new DefaultThing[] { new DefaultThing(), new DefaultThing() };

JObject[] castSuccess = (JObject[])collectionImpl; // This should be fine

JObject[] castFail = (JObject[])collection; // This should throw a System.ClassCastException