Map

(Map don't allow duplicate key)

Types of Map:

• HashMap - unordered
• LinkedHashMap - ordered
• TreeMap (Sorted Map) - sorted by key

Instantiate

Map<datatype, datatype> map = new HashMap <datatype, datatype> ();

Methods (map)

• put() - to insert/ update key,value pair in map

  map.put(key,value);

  //To add entire map to another

  map.putAll(Map map);

• get() - to fetch the value of a key from map

  dataype value = map.get(key);

• remove() - to remove the pair from the map

  map.remove(key);

• size() - returns number of key/value pairs available in the map.

  int n = map.size();

• containsKey() - returns true if key is present in the map

  boolean map.containsKey(key);

• containsValue() - returns true if value is present in the map

  boolean map.containsValue(value);

• keySet() - returns set view of map of all keys

  Set set = map.keySet();

• values() - It returns a Collection view of the values contained in this map.

  List l = map.values();

• entrySet() - method returns a complete set of keys and values present in the Map.

  Set<Map.Entry<datatype, datatpe>> set = map.entrySet();

• Traversing Map

  // Traversing through the Map

  for (Map.Entry<datatype, datatype> me : map.entrySet()) {

  System.out.print(me.getKey() + ":");

  System.out.println(me.getValue());

  }