Is there a better way to combine two string sets in java?

Question

I need to combine two string sets while filtering out redundant information, this is the solution I came up with, is there a better way that anyone can suggest? Perhaps something built in that I overlooked? Didn't have any luck with google.

Set<String> oldStringSet = getOldStringSet(); Set<String> newStringSet = getNewStringSet();  for(String currentString : oldStringSet) {     if (!newStringSet.contains(currentString))     {         newStringSet.add(currentString);     } } 

Answer 1

Since a Set does not contain duplicate entries, you can therefore combine the two by:

newStringSet.addAll(oldStringSet); 

It does not matter if you add things twice, the set will only contain the element once... e.g it's no need to check using contains method.

Answer 2

You can do it using this one-liner

Set<String> combined = Stream.concat(newStringSet.stream(), oldStringSet.stream())         .collect(Collectors.toSet()); 

With a static import it looks even nicer

Set<String> combined = concat(newStringSet.stream(), oldStringSet.stream())         .collect(toSet()); 

Another way is to use flatMap method:

Set<String> combined = Stream.of(newStringSet, oldStringSet).flatMap(Set::stream)         .collect(toSet()); 

Also any collection could easily be combined with a single element

Set<String> combined = concat(newStringSet.stream(), Stream.of(singleValue))         .collect(toSet());