非泛型类中的通用方法

Question

I am trying to use a generic method so I don't have to repeat code. I have tried:

private Listener createListenerAdapter(Class<T> clazz)
{ 
   // do something
}

( clazz being important because class is reserved).

But Netbeans complains that : "Cannot find symbol class T".

I am going to be passing in a few different classes that have the same methods on them. Where am I supposed to define T?

Answer 1

Declare the method as:

private <T> Listener createListenerAdapter(Class<T> clazz)

See the Java Tutorials for more information.

Edit: If T isn't related to the return type you could also just use a wildcard:

private Listener createListenerAdapter(Class<?> clazz)

Edit 1: If clazz is meant to represent a type of Listener , you could define bounds to restrict the caller (to avoid casts and potential runtime exceptions):

private <L extends Listener> L createListenerAdapter(Class<L> clazz)

Or with the wildcard:

private Listener createListenerAdapter(Class<? extends Listener> clazz)

But that depends on how clazz is used in the body.

Answer 2

Generic declarations can also be made at method-level by parametrizing them like this:

private <T> Listener createListenerAdapter(Class<T> clazz)
{ 
   // do something
}

Answer 3

If you're not using the type (unlikely, but you may be trying to avoid a raw type warning):

private Listener createListenerAdapter(Class<?> clazz)
{ 
   // do something, without knowing the T of the clazz
}