Java Iteration over a keySet

I have the following Java code:

public void myMethod (final Map pFeatureGroupsFromPackage) {

   final Set<String> keys = pFeatureGroupsFromPackage.keySet();

   for (final String key : keys) {
           tmpList = (List<FeatureKey>) pFeatureGroupsFromPackage.get(key);
    // do whatever
   }
}

I am getting a warning from "findBugs" telling the following:

Method myMethod makes inefficient use of keySet iterator instead of entrySet iterator. The warning is done at the tmpListassignment.

I do not understand why this is inefficient. In fact the keyslist is computed only once. Any comment? Thanks.

Instead of iterating over the keySet and calling get to get the corresponding value for each key, iterate over the entrySet:

final Set<Map.Entry<String, List<FeatureKey>>> entries = pFeatureGroupsFromPackage.entrySet();

for (Map.Entry<String, List<FeatureKey>> entry : entries) {
    String key = entry.getKey();
    List<FeatureKey> tmpList = entry.getValue();

    // do whatever
}

That way you don't have to do a lookup in the map for every key; you directly get the key and value in one go.

Also, declare your Map with type parameters:

public void myMethod (final Map<String, List<FeatureKey>> pFeatureGroupsFromPackage) {
    // ...
}