4. Sets and Maps

4.1 - Sets

• Set extends Collection
• An set can contain NO duplicates.
• Hashset
  • Capacity is doubled when the (capacity * load factor) is reached
    • Load Factor is number between 0.00 and 1.00
    • The bigger the load factor decreases space costs, but increases search time. (0.75 is a good middle)
  • Used to store duplicate-free items.
  • Objects added to a hash-set needs to implement the hashCode.
  • No order is imposed.
  • Use for-each to traverse all elements in the list.
  • All methods from Collection can be used.
• LinkedHashSet
  • Hashset with an linked list implementation to support ordering of items.
  • Remembers the order in which te items are inserted, does not store duplicates.
• TreeSet
  • SortedSet is a subinterface of set, which guarentees that the items are sorted.
  • NavigableSet implements SortedSet to provide navigation methods.
  • TreeSet implements SortedSet,
  • If an TreeSet is create with the no-arg constructor the compareTo from the object is used (which implement Comparable)

4.2 - Maps

• Map = Container object athat stores a collection of key/value pairs.
• Fast retrieval, deletion, updating of the pair through the key.
• Map methods:
  • Clear
  • ContainsKey/Value - True if this map contains an entry for the specified key.
  • EntrySet - Set consisting of all entries in the map.
  • Get
  • IsEmpty
  • KeySet- Returns a set containing all keys.
  • Put(all)
  • Remove
  • Size
  • Values - Returns a collection consisting of the values in the map.
• Entry methods:
  • getKey
  • getValue
  • setValue
• Concrete Implementations
  • HashMap (no duplicates)
    • Efficient for locating/inserting/deleting entry.
  • LinkedHashMap (no duplicates, ordering)
    • Sorted in insertion order, or access order (least recent to most recent)
  • TreeMap (no duplicates, sorted)
    • Efficient for traversing the keys in a sorted order.
  • SortedMap
  • NavigableMap