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 som

Answer 1

From the definition Set contain only unique elements.

Set<String> distinct = new HashSet<String>(); 
 distinct.addAll(oldStringSet);
 distinct.addAll(newStringSet);

To enhance your code you may create a generic method for that

public static <T> Set<T> distinct(Collection<T>... lists) {
    Set<T> distinct = new HashSet<T>();

    for(Collection<T> list : lists) {
        distinct.addAll(list);
    }
    return distinct;
}

Answer 2

The same with Guava:

Set<String> combinedSet = Sets.union(oldStringSet, newStringSet)

Answer 3

Set.addAll()

Adds all of the elements in the specified collection to this set if they're not already present (optional operation). If the specified collection is also a set, the addAll operation effectively modifies this set so that its value is the union of the two sets

newStringSet.addAll(oldStringSet)

Answer 4

 newStringSet.addAll(oldStringSet);

This will produce Union of s1 and s2

Answer 5

http://docs.oracle.com/javase/7/docs/api/java/util/Set.html#addAll(java.util.Collection)

Since sets can't have duplicates, just adding all the elements of one to the other generates the correct union of the two.

Answer 6

If you care about performance, and if you don't need to keep your two sets and one of them can be huge, I would suggest to check which set is the largest and add the elements from the smallest.

Set<String> newStringSet = getNewStringSet();
Set<String> oldStringSet = getOldStringSet();

Set<String> myResult;
if(oldStringSet.size() > newStringSet.size()){
    oldStringSet.addAll(newStringSet);
    myResult = oldStringSet;
} else{
    newStringSet.addAll(oldStringSet);
    myResult = newStringSet;
}

In this way, if your new set has 10 elements and your old set has 100 000, you only do 10 operations instead of 100 000.