CODEWITHSUNDEEP
javagenerics
ExiRe
ExiRe

Reputation: 4767

Java generics - gain access to parameters

I have next code:

class iCache<K,V> implements Map<Object, Object>
{
...//Code
}

How can I get the class name of K and V?

Upvotes: 3

Views: 112

Answers (5)

Enno Shioji
Enno Shioji

Reputation: 26882

If you extend iCache and want to obtain the typer parameters you used to declare the subclass (like below):

class someCache extends iCache<Integer,Long> {
//...
}

You can find out those parameters at runtime using the following (source):

Class clazz = ((ParameterizedType) getClass()
                       .getGenericSuperclass()).getActualTypeArguments()[0];

If you provide the parameters at instantiating like this

iCache<Integer,Long> cache = new iCache<Integer,Long>();

then you are out of luck (more info).

Upvotes: 3

RedSoxFan
RedSoxFan

Reputation: 634

Actually you can, call the getClass() method on the key and value

Upvotes: 0

Chris Dennett
Chris Dennett

Reputation: 22741

The types will get erased. Pass in Class and Class as args into the constructor to pass through your raw types. Store as fields. Note: your patameterisation is bad anyway: you need to pass K and V to Map as well, or you'll give yourself more pain.

Upvotes: 2

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272772

You can't. Java generics don't work that way. At runtime, there is no class-specific information available (this is known as erasure). If you really need this information, you will have to pass in e.g. Class objects.

Upvotes: 5

mmccomb
mmccomb

Reputation: 13817

You can't, the compiler performs type erasure at compile time. In other words, the K and V type parameters are purely a compile time notion, they aren't accessible at runtime.

What you can do is to grab the class of the key/values in your custom Map type at runtime.

Upvotes: 7

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