/**
* Returns any duplicate elements from the given collection.
*
* @param <T> the generic type of the given collection.
* @param c the given collection that might have duplicate elements.
* @return a collection containing the duplicate elements of the given one. If no duplicates are
* found, an empty collection is returned.
*/
public static <T> Collection<T> duplicatesFrom(Collection<T> c) {
Set<T> duplicates = new HashSet<T>();
if (isEmpty(c)) return duplicates;
Set<T> onlyOne = new HashSet<T>();
for (T e : c) {
if (onlyOne.contains(e)) {
duplicates.add(e);
continue;
}
onlyOne.add(e);
}
return duplicates;
}
/**
* Creates a set containing the given elements.
*
* @param <T> the type of elements of the set to create.
* @param elements the elements to store in the set.
* @return the created set.
* @since 1.1.5
*/
public static <T> Set<T> set(T... elements) {
if (elements == null) return null;
Set<T> set = new LinkedHashSet<T>();
for (T e : elements) set.add(e);
return set;
}