Re: Generics: how to read actual type parameters
- From: Lew <lew@xxxxxxxxxxxxx>
- Date: Sun, 30 Sep 2007 16:24:30 -0400
Joshua Cranmer wrote:
marek.dudek@xxxxxxxxx wrote:For example:1. Don't use tabs in Usenet posts.
public class Pair<S> {
public String toString() {
Class clas = ??? ;
return "Pair of " + clas.toString();
}
public S first;
public S second;
}
2. What you are probably intending to do is impossible as specified. There is no possible way at runtime to get the class of S. Java erases the types of the parameters at runtime.
3. Class is generic. Use Class<?> instead.
The easiest thing you can do is:
Class<?> clas = first.getClass();
A potentially tighter bound is:
Class<?> left = first.getClass();
Class<?> right = second.getClass();
Class<?> clas = left;
while (!clas.isAssignableFrom(right))
clas = clas.getSuperclass();
(This returns the last common ancestor of the classes of first and second)
Another hack in a class you own is to have a Class<?> instance variable to provide runtime type information.
And here's a recent article I just googled up that delves into the issue (GIYF):
<http://www.artima.com/weblogs/viewpost.jsp?thread=208860>
--
Lew
.
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- From: marek . dudek
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- From: Joshua Cranmer
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