TreeMap question#2

[Anthony Alexander]

Say I have two treemaps A and B defined as : <String, Integer>

eg.

Tree Map A
-----------
apple, 4
orange, 2

Tree Map B
-----------
banana, 3
orange, 1


How do I search for identical keys (orange in this example) and use the values for each key (eg. 2 + 1 = 3)?

Do I have to loop through every treemap looking at every key?

[Keith Lynn]

If you look at the API for TreeMap, there is a method keySet which will return a Set containing the keys in the TreeMap.

In the Set interface there is a specification for the method retainAll which will produce the intersection of two sets.

[Garrett Rowe]

If you are only interested in keys that are identical to both TreeMaps then you can use the retainAll() method.

Assumiing you have two treeMaps that you want to find the identical keys for.

 
Set<String> map1Keys = map1.keySet();
Set<String> map2Keys = map2.keySet();
 
//Add all of either set into a Set that will hold matching keys
Set<String> matchingKeys = new HashSet<String>(map1Keys);
//Now call retainAll() to retain only the keys that exist in both sets
matchingKeys.retainAll(map2Keys);
 
//Now you can use these keys to iterate the sets
for (String key : matchingKeys)
{
   Integer map1Result = map1.get(key);
   Integer map2Result = map2.get(key);
 
   int total = map1Result + map2Result;
 
   System.out.println("Total for " + key + " = " total);
}

[Anthony Alexander]

Yes. Yes. Good idea. that may work. thanks.