Difference between Iterator and Listitrerator

 Iterator

• Iterator is used to traverse Set and List and also Map type of Objects.
• Iterator is used retrieve the elements from Collection Object in forward direction only.

Listiterator

• List Iterator can be used to traverse for List type Objects, but not for Set type of Objects.
• List Iterator, which allows you to traverse in two directions.
• So it has another methods hasPrevious() & previous() other than Iterator.

Difference between ArrayList and Vector

ArrayList 

• It cannot be synchronized

Vector

• It can be synchronized

Map Interface

• Map
• Map.Entry
• NavigableMap
• SortedMap

Map Classes

Map - Have a key and value

• HashMap
• LinkedHashMap
• TreeMap

Collection Classes

Important Collection classes:
List - Duplicate objects can be loaded

• ArrayList implements List
• LinkedList implements List,Queue,Deque

Set - Duplicate objects cannot be loaded

• HashSet implements Set - (It does not guarantee the order of its elements)
• LinkedHashSet - (It ensures the order in which it is inserted)
• TreeSet implements NavigableSet - (Objects are stored in sorted, ascending order)
• PriorityQueue
• ArrayDeque - (It can be used as a stack)

Note:
peek() - return and removed

poll() - return but does not removed

Collection framework Interfaces

Collection framework interfaces are:

• Collection
• List (Duplicate Objects can be loaded)
• Queue
• Dequeue
• Set (No Duplicate objects)
• SortedSet (Objects are sorted)
• Navigable Set