THE Java™ Programming Language, Fourth Edition

process(list.get(i));

will typically be faster than using

Iterator it = list.iterator();
while (it.hasNext())
process(it.next());

then your list should implement RandomAccess.

21.7. Queue

The Queue interface extends Collection to add some structure to the internal organization of the
collection. A queue defines a head position, which is the next element that would be removed. Queues often
operate on a first-in-first-out ordering, but it is also possible to have last-in-first-out ordering (commonly
known as a stack) or to have a specific ordering defined by a comparator or by comparable elements. Each
implementation must specify its ordering properties. The Queue interface adds several methods that work
specifically with the head:

public Eelement()

Returns, but does not remove, the head of the queue. If the queue is empty a

NoSuchElementException is thrown.

public Epeek()

Returns, but does not remove, the head of the queue. If the queue is empty,

null is returned. This differs from element only in its handling of an

empty queue.

public Eremove()

Returns and removes the head of the queue. If the queue is empty a

NoSuchElementException is thrown.

public Epoll()

Returns and removes the head of the queue. If the queue is empty, null is

returned. This differs from remove only in its handling of an empty queue.

There is also a method for inserting into a queue:

public booleanoffer(E elem)

Attempts to insert the given element into this queue. If the attempt is

successful, true is returned, otherwise false. For queues that have

genuine reason to reject a requestsuch as a queue with finite capacitythis

method is preferable to the Collectionadd method which can only

indicate failure by throwing an exception.