Intersection of java.util.Map
How about:
Map map1 = ...;
Map map2 = ...;
Map result = new ...(map1);
result.keySet().retainAll(map2.keySet());
or:
Map map1 = ...;
Map map2 = ...;
Set result = new ...(map1.keySet());
result.retainAll(map2.keySet());
If you're using Guava, you can use Maps.difference to get a MapDifference object, from which you can extract the entriesInCommon() and entriesDiffering() as maps. (Disclosure: I contribute to Guava.)
Guava's Sets.intersection(Set, Set) should do the job, with the keySet of each Map passed in as parameters.