itech9

Collections characteristics:

• synchronized (hashtable-yes, hashmap-no, vector-yes, arraylist-no)
• directionality (iterators)
• allow null values (hashtable-no, hashmap-yes)
• preserve insert order
• duplicates (set-no, list-yes)

Notes:

• Collections interfaces: Collection, Set, List and Map.
• To synchronize HashMap:

  Map m = Collections.synchronizeMap(hashMap);

• Some implementations: HashSet, HashMap, ArrayList, LinkedList, TreeSet and TreeMap.
• An ArrayList is resizable, where as, an array is not.
• Hashmap overrides?

  The methods to override are equals() and hashCode().

• Difference between Enumeration and Iterator?

  Enumeration is read-only. Iterator provides remove and add methods
  and it is fail-fast in multi-threaded configurations.