 | Session 13 |  |
Map
A map (in Python - dictionary) is an object that stores associations between keys and values (key/value pairs). The keys are like indexes. In Map, the keys are integers, strings or any type of objects. A map cannot contain duplicate keys. Each key maps to one value. A key and its corresponding value form an entry stored in a map. Maps enable fast retrieval, deletion, and updating of pairs through keys.
One of the most useful map classes is HashMap.
The following example simulates a telephone book:
Map<String, Integer> telephoneBook = new HashMap<>();
telephoneBook.put("Peeter Peet", 5562356);
telephoneBook.put("Mari Maasikas", 53438956);
System.out.println("Mari's number is " + telephoneBook.get("Mari Maasikas"));
Note: a map has two generic types in the angle brackets: one for the key (String) and one for its value (Integer).
Also note that get returns the null value if the map contains no mapping for the key.
| Session 13 | |