Java HashMaps

HashMap hashMapName = new HashMap();


HashMap hashMapName = new HashMap(5);
//The 5 sets the initial element capcaity.


HashMap hashMapName = new HashMap(5, .9);
//The 5 sets the initial element capcaity.
//The .9 is the load factor.  
//  The default load factor is .75.


HashMap hashMapName = new HashMap(mapIn);
//creates a new HashMap with the elements of a map.

int HashMapSize = hashMapName.size();


boolean isHashMapEmpty = hashMapName.isEmpty();


boolean isObjectKeyInHashMap = 
  hashMapName.containsKey(objectToSearchForAsKey);


boolean isObjectValueInHashMap = 
  hashMapName.containsValue(objectToSearchForAsValue);

Object objectName = 
  (ClassTypeToCastTo) hashMapName.get(keyToGetObjectValueFor);
  //note: Objects coming out of HashMaps have lost 
  //  their class type, and must be cast


Set setOfAllKeys = hashMapName.keySet();
  //The set is a "view", 
  //  so changes to the original HashMap change the view, 
  //  and changes to the view change the original HashMap.


Collection collectionOfAllValues = hashMapName.values();
  //The collection is a "view", 
  //  so changes to the original HashMap change the view, 
  //  and changes to the view change the original HashMap.


Set setOfAllEntryValues = hashMapName.entrySet();
  //note: "Returns a collection view of the mappings 
  //  contained in this map" 
  //  (Platform API Spec, See online refs)
  //The collection is a "view", 
  //  so changes to the original HashMap change the view, 
  //  and changes to the view change the original HashMap.


Object cloneOfHashMap = hashMapName.clone();
  //Shallow copy of HashMap, 
  //  objects in HashMap are not cloned. 

Object objectReplacedForKey = 
  hashMapName.put(objectKey, objectToAdd);
  //inserts object value for a specified key
  //returns the object that is replaced for that key, 
  //  null if nothing is repplaced


hashMapName.putAll(mapToAdd);
  //adds a map into the HashMap


hashMapName.remove(keyObject);
  //removes a key and value pair for a key


hashMapName.clear();