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JDK1.5 Generic Class Cast problem..

zollen
zollen asked
on
Medium Priority
690 Views
Last Modified: 2011-04-14
Map<?, ?> map = (Map<?, ?>) req.getParameterMap();

Set<String> set = (Set<String>) map.keySet();

=========================

I received the following compilatio warning:

warning: [unchecked] unchecked cast
found   : java.util.Set<capture of ?>
required: java.util.Set<java.lang.String>
                Set<String> set = (Set<String>)map.keySet();

===========
How do I get rid of this warning??
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Top Expert 2006

Commented:
Because of Map<?, ?>
You can only say
Set<?> set = (Set<?>) map.keySet();
CERTIFIED EXPERT
Top Expert 2016

Commented:
Try

java.util.Enumeration<String> enum = req.getParameterNames();

or

java.util.Enumeration<String> enum = (java.util.Enumeration<String>)req.getParameterNames();
Top Expert 2006

Commented:
CEHJ there is no Generics support in javaee according to the documentation
http://java.sun.com/javaee/5/docs/api/javax/servlet/ServletRequest.html#getParameterMap()
All collections are being used like traditional non-generic form
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Top Expert 2016

Commented:
That's true

Commented:
Since the J2EE specs do not return generalized (?) Maps, the best you can do is annotate your method with SuppressWarnings to tell the compiler to ignore the warning.

http://java.sun.com/j2se/1.5.0/docs/api/java/lang/SuppressWarnings.html

Commented:
I'm not saying that it will work at runtime, though...  You still might get a ClassCastException.
Commented:
@SuppressWarnings("unchecked")
void yourMethod() {
    Map<?, ?> map = (Map<?, ?>) req.getParameterMap();
    Set<String> set = (Set<String>) map.keySet();
}

cf. http://java.sun.com/docs/books/tutorial/java/javaOO/annotations.html

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