bloganesh: Collections: Queue(s)

Are thread safe
Blocks the thread which tries to dequeue elements from an empty queue OR a thread which tries to insert elements in queue which is already full
Threads are blocked until an element is either inserted or removed respectively
Do not accept NULL values
Used to implement producer/consumer based application
If operation is not possible immediately then (refer below table)

	Throws Exception	Returns Special Value usually (true/false)	Blocks method call	Method call blocks & waits till Time Out
Insert	add(o)	offer(o)	put(o)	offer(o, timeout, timeunit)
Remove	remove(o)	poll()	take()	poll(timeout, timeunit)
Examine	element()	peek()

Elements are inserted according to some priority order (not FIFO)
Either default natural sorting order or customized sorting order can be implemented
Insertion order not preserved
Duplicates are not allowed
Heterogeneous objects allowed ONLY for customized order, ONLY homogeneous for natural sorting order
NULL elements NOT allowed
Constructors
Default: With initial capacity 11 and with natural sorting order
int initialCapacity = Creates with predefined size = initialCapacity
int initialCapacity, Comparator c: Creates with predefined size = initialCapacity and comparator for customized sorting
SortedSet s: convert SortedSet to PriorityQueue
Collection c: convert Collection to PriorityQueue
Some Operating Systems won’t provide proper support for thread priorities and PriorityQueue

Implements List -> Collection
Insertion order preserved, Allows: Duplicates, Heterogeneous objects & null
By default LinkedList creates Empty list, memory allocation is done at runtime
Constructors
Default
Collections C = convert any collection to LinkedList
Highly recommended when there are frequent random insert or deletes
Not recommended when there are frequent retrieval operations as it needs rearranging the indexes
LinkedList provides a few methods like addFirst, addLast, RemoveFirst, removeLast, getFirst & getLast to support Stack & Queue based implementation using LinkedList
Version 1.5 onwards LinkedList also implements Queue interface, such LinkedList implementation will always follow FIFO order

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