Question

I want to check if a given Class is assignable to a java.util.Collection, and if so create a new instance of it.

I tried the following:

Class<?> clazz = ... // I got this from somewhere

if (!clazz.isInterface() && java.util.Collection.class.isAssignableFrom(clazz)) {
    java.util.Collection<?> collection = clazz.newInstance();
}

Predictably it doesn’t work, since it cannot convert to an unknown type to a java.util.Collection.
I thought of adding a cast but that seems like a hack.

I also thought of doing this:

Class<? extends java.util.Collection<?>> collectionClass = Class<? extends java.util.Collection<?>> clazz;
java.util.Collection<?> collection = clazz.newInstance();

Now there’s no need for the cast at newInstance but I still have to cast the Class object.

What’s the right way to do this? Thanks.

(for clarity I removed the try/catch around newInstance in case I’m trying to instantiate an abstract class)

Answer 1

Cast is a must because of the wild card you are using. i.e. Class<?> clazz. Casting is not a hack, c’mon. And here its reasonably fine, as its under the check.