Hashmap

Creating a HashMap

HashMap<Integer, String> myHashMap = new HashMap<Integer, String>();

Key class methods

• put(KeyType key, ValueType value) add key value pair

  hmap.put(12, "Chaitanya");
  

• get(key) retrieve value by key

hmap.get(2);
// or
hmap.get(myKey);

• remove(key) remove key-value pair by key

hmap.remove(3);

• void clear() It removes all the key and value pairs from the specified Map.
• Object clone() It returns a copy of all the mappings of a map and used for cloning them into another map.
• boolean containsKey(Object key) It is a boolean function which returns true or false based on whether the specified key is found in the map.
• boolean containsValue(Object Value) Similar to containsKey() method, however it looks for the specified value instead of key.
• Value get(Object key) It returns the value for the specified key.
• boolean isEmpty() It checks whether the map is empty. If there are no key-value mapping present in the map then this function returns true else false.
• Set keySet() It returns the Set of the keys fetched from the map.
• value put(Key k, Value v) Inserts key value mapping into the map. Used in the above example.
• int size() Returns the size of the map – Number of key-value mappings.
• Collection values() It returns a collection of values of map.
• Value remove(Object key) It removes the key-value pair for the specified key. Used in the above example. void putAll(Map m): Copies all the elements of a map to the another specified map.

Displaying content (using iterator)

import java.util.Iterator;
/* Display content using Iterator*/
      Set set = hmap.entrySet();
      Iterator iterator = set.iterator();
      while(iterator.hasNext()) {
         Map.Entry mentry = (Map.Entry)iterator.next();
         System.out.print("key is: "+ mentry.getKey() + " & Value is: ");
         System.out.println(mentry.getValue());
      }