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