Re: Casting an object to a genericized TreeMap

From:

Daniel Pitts <googlegroupie@coloraura.com>

Newsgroups:

comp.lang.java.programmer

Date:

3 May 2007 18:14:53 -0700

Message-ID:

<1178241293.644638.234230@h2g2000hsg.googlegroups.com>

On May 3, 6:41 am, "Kaiser S." <sau...@name.invalid> wrote:

Ingo R. Homann a =E9crit :

Hi,

Kaiser S. wrote:

What do you think of this code ? Is there a better way do enforce this
kind of cast ?

    public static <K, V> TreeMap<K, V> treemap(Object o, Class<K>
keyClass, Class<V> valueClass) {
        TreeMap<?, ?> tm = (TreeMap)o; // warning 1
               for (Map.Entry<?, ?> couple : tm.entrySet()) {
            keyClass.cast(couple.getKey());
            valueClass.cast(couple.getValue());
        }
        return (TreeMap)o; // warning 2
    }

called with:

TreeMap<String, Double> tm = treemap(o, String.class, Double.class);

You know that your code does not do anything, and that the following
would do exactly the same?

public static <K, V> TreeMap<K, V> treemap(Object o) {
return (TreeMap<K,V>)o; // warning
}

Well i hope not. I check the class of all the keys and values; you must
have seen it...

Now the doc of Class.cast says it throw a ClassCastException if the cast
is invalid, so after the for loop, i can make the ugly cast because i'm
sure i won't get a ClassCastException somewhere else in my program.

If you really want to check the types, I suggest using instanceof
I'm kind of curious why you go through the effort. Whats going on that
you have a TreeMap object thats not in a TreeMap type reference?