How do I address unchecked cast warnings?

Question

Eclipse is giving me a warning of the following form:

Type safety: Unchecked cast from Object to HashMap

This is from a call to

Answer 1

In the HTTP Session world you can't really avoid the cast, since the API is written that way (takes and returns only Object).

With a little bit of work you can easily avoid the unchecked cast, 'though. This means that it will turn into a traditional cast giving a ClassCastException right there in the event of an error). An unchecked exception could turn into a CCE at any point later on instead of the point of the cast (that's the reason why it's a separate warning).

Replace the HashMap with a dedicated class:

import java.util.AbstractMap;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class Attributes extends AbstractMap {
    final Map content = new HashMap();

    @Override
    public Set> entrySet() {
        return content.entrySet();
    }

    @Override
    public Set keySet() {
        return content.keySet();
    }

    @Override
    public Collection values() {
        return content.values();
    }

    @Override
    public String put(final String key, final String value) {
        return content.put(key, value);
    }
}

Then cast to that class instead of Map and everything will be checked at the exact place where you write your code. No unexpected ClassCastExceptions later on.