book 'Java Persistence With Hibernate' page 143 - FAQ

chhasid · **Joined:** Wed Nov 29, 2006 5:53 pm **Posts:** 1

In the FAQ on this page its stated -

Quote:

However, item1 and item2 are Java Map instances,
and the equals() implementation of a map is based on the key sets of
the map.

This statement is false cos in JDK5 AbstractMap.java implements equals thus

Code:

 public boolean equals(Object o) {
   if (o == this)
       return true;
   if (!(o instanceof Map))
       return false;
   Map<K,V> t = (Map<K,V>) o;
   if (t.size() != size())
       return false;
        try {
            Iterator<Entry<K,V>> i = entrySet().iterator();
            while (i.hasNext()) {
                Entry<K,V> e = i.next();
      K key = e.getKey();
                V value = e.getValue();
                if (value == null) {
                    if (!(t.get(key)==null && t.containsKey(key)))
                        return false;
                } else {
                    if (!value.equals(t.get(key)))
                        return false;
                }
            }
        } catch(ClassCastException unused) {
            return false;
        } catch(NullPointerException unused) {
            return false;
        }

   return true;
    }

So this implementation of equals does look at and compare values also(not just keys as stated).
Am i missing something here or not understanding what the author meant ??

christian · **Posted:** Wed Nov 29, 2006 6:21 pm

Well, you might be right and I might be wrong in what I said. In practice it doesn't work with two HashMap instances and the code in the examples. It looked to me like an equals() problem, but I only spend an hour or so on it.

If you can make the examples work, I'd be happy to post an errata.