Java Iteration over a keySet

Question

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.

Answer 1

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) {
    // ...
}