Check if is specific type instance for parameterised type

Question

I have a method with an template parameter:

public CustomClass getData(Class<? extends InterfaceA> item) {  

}

I have ended up with one case that this can be called with an item that can be an inner anonymous class that adheres to the class expected but how can I know when I got this object inside my method?
If I do if(item.equals(ConcreteA.class)) where ConcreteA is the usual class that works it fails.
Also if I use class name I need to use something like:
item.getName().equals(“com.a.b.Utils$1”);

How can I check the instance in this case?

You're missing the getClass() on item. I.e. if (item.equals.getClass()(ConcreteA.class)). Still, I don't understand your problem. Why is it important to check for class-equality? What do you want to achieve with this? — Tamas Rev
– Tamas Rev, Commented Jun 30, 2016 at 10:28

ernest_k · Accepted Answer · 2016-06-30 09:08:29Z

1

You need to check whether the types are compatible, i.e., whether InterfaceA is a supertype of item:

boolean isValidType = InterfaceA.class.isAssignableFrom(item)

API Docs: https://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#isAssignableFrom(java.lang.Class)

answered Jun 30, 2016 at 9:08

ernest_k

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2 Comments

Andy Turner Over a year ago

If item is of type Class<? extends InterfaceA>, wouldn't isValidType always be true?

ernest_k Over a year ago

@AndyTuner: In theory, yes: at compile time, and assuming the code calling this method is generic. But there's no such guarantee at runtime (type erasure). Calls could also be using reflection... But there's a reason for the check needed by Jim.

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