 | Chapter 12 |  |
Set
A Set is a collection that cannot contain duplicate elements. There are three main implementations of the Set interface:
HashSet, which stores its elements in a hash table, is the best-performing implementation; however it makes no guarantees concerning the order of iteration;TreeSet, which stores its elements in a red-black tree, orders its elements based on their values; it is substantially slower than HashSet;LinkedHashSet, which is implemented as a hash table with a linked list running through it, orders its elements based on the order in which they were inserted into the set (insertion-order).
The main methods of any set are:
add- adds an element to the set if it is not already present;contains- checks if the element is present in the set.
Set<String> myMails = new HashSet<>();myMails.add("example@example.com");myMails.add("java-is-awesome@example.com");myMails.add("example@example.com"); // the address won't be added; it is present in the setfor (String address : myMails) { System.out.println(address);}List<String> names = Arrays.asList("Anna", "John", "Aivar", "Marina", "Aivar");// get a set with unique elementsSet<String> uniqueNames = new HashSet<>(names); // convert the set into a listnames = new ArrayList<>(uniqueNames); |
Usually sets are used to get a collection of unique elements or to find the intersection, the union ja the difference (theory of sets ).
| Chapter 12 | |