Accessing the data type of a Generic structure
Good afternoon, Ladies and Gentlemen!
So, I've got this method loadStuff, that I want to be able to take as input a Hashtable that maps Strings to other things. Right now, my method definition looks like:staticint loadStuff(File infile, Hashtable<String, ?> Storage)
but I get a compile time error
"cannot find symbol
symbol : method put(java.lang.String,StatsRecord)
location: class java.util.Hashtable<java.lang.String,capture of ?>
Storage.put(PreHash.getname(), PreHash);"
Is there a way around this?
Also: I'd like some way to get at the type of hashtable that I'm passing to the function. So what I'm looking for would be a method that, if I passed it Awesome =new List<AwesomeClass>()
would return AwesomeClass.
Any thoughts?
Concerning compilation error:
You are trying to put (write) data to your Storage hashtable.
But
Storage.put("I磎 a string", new StatsRecord());
is not allowed with wildcarded types. Read Angelika Langer's FAQ for this.
Way around: do not use unbounded wildcard. Use bounded wildcards instead (this won磘 be sufficient in your case). Use concrete parametrized types, that is Hashtable<String, Integer> f.e.
Concerning AwesomeClass:
as far as I know, there is no way to obtain generics type information during runtime, since nearly all of that information is removed due to "type erasure"
The only thing you could do is a parameterized method (doesn't have to be static)
Class cool {
....
void <U> methodName(Class<U> clazz, List<U> list) {
// use reflection here f.e.
// clazz.isInstance(..)
}
}
A call to this method could be:
Cool veryCoolInstance = new Cool();
veryCoolInstance.<Integer>methodName(Integer.class, yourList);
Best regards
DTN
