Question

I get a warning about unchecked casts on the “return (T) value;” line. Is there a better way to do this, or should I just suppress the warning?

class SomeClass<T>
{
    /* ... other methods ... */

    private Set<T> aSet;
    public T filter(Object value)
    {
        if (this.aSet.contains(value))
            return (T) value;
        else
            return null;
    }
}

edit: I’m stuck with public T filter(Object value) as a signature.

Answer 1

Elaborating on Tom Hawtin’s answer, you have the option of using a Map<T,T> instead, which gets around the casting issue. If you’re using a HashSet<T> for aSet‘s implementation, HashSet uses a HashMap<T,HashSet<T>> behind the scenes anyway (it uses references to itself as the values – not sure if there’s a reason for this other than choice – with the set’s “values” as keys) and performs the bulk of its operations just by reinterpreting the return values of the Map functions.

Consequently, you could do this, if you wanted to (and I don’t see an immediate reason why it would be any less performant than a HashSet):

class SomeClass<T>
{
    /* ... other methods ... */

    private Map<T,T> aSet;

    public T filter(Object value)
    {
        // Will return the properly-typed object if it's in
        // the "set" otherwise will return null
        return aSet.get(value);
    }
}