How to compare two maps by their values

The correct way to compare maps for value-equality is to:

1. Check that the maps are the same size(!)
2. Get the set of keys from one map
3. For each key from that set you retrieved, check that the value retrieved from each map for that key is the same (if the key is absent from one map, that's a total failure of equality)

In other words (minus error handling):

boolean equalMaps(Map<K,V>m1, Map<K,V>m2) {
   if (m1.size() != m2.size())
      return false;
   for (K key: m1.keySet())
      if (!m1.get(key).equals(m2.get(key)))
         return false;
   return true;
}

Your attempts to construct different strings using concatenation will fail as it's being performed at compile-time. Both of those maps have a single pair; each pair will have "foo" and "barbar" as the key/value, both using the same string reference.

Assuming you really want to compare the sets of values without any reference to keys, it's just a case of:

Set<String> values1 = new HashSet<>(map1.values());
Set<String> values2 = new HashSet<>(map2.values());
boolean equal = values1.equals(values2);

It's possible that comparing map1.values() with map2.values() would work - but it's also possible that the order in which they're returned would be used in the equality comparison, which isn't what you want.

Note that using a set has its own problems - because the above code would deem a map of {"a":"0", "b":"0"} and {"c":"0"} to be equal... the value sets are equal, after all.

If you could provide a stricter definition of what you want, it'll be easier to make sure we give you the right answer.