Queues typically, but do not necessarily, order elements in a - * FIFO (first-in-first-out) manner. Among the exceptions are priority - * queues, which order elements according to a supplied comparators, or - * the elements natural ordering. Every Queue implementation must specify - * its ordering guarantees. + * FIFO (first-in-first-out) manner. Among the exceptions are + * priority queues, which order elements according to a supplied + * comparator, or the elements' natural ordering. Every Queue + * implementation must specify its ordering guarantees. * *
The {@link #offer(E)} method adds an element if possible, otherwise * returning false. This differs from the {@link @@ -23,13 +23,18 @@ package java.util; * failure. It is designed for use in collections in which failure to * add is a normal, rather than exceptional occurrence, for example, * in fixed-capacity (or “bounded”) queues. + * - *
The {@link #remove()} and {@link #poll()} methods remove and return an - * element in accord with the implementation's ordering policy. For example, - * in FIFO queues, they remove and return the oldest element in the queue. - * The remove() and poll() methods differ only in their - * behavior when the queue is empty: the remove() method throws an - * exception, while the poll() method returns null. + *
The {@link #remove()} and {@link #poll()} methods remove and + * return an element in accord with the implementation's ordering + * policy. Exactly which element is removed from the queue is a + * function of the queue's ordering policy, which differs from + * implementation to implementation. Possible orderings include (but + * are not limited to) first-in-first-out (FIFO), last-in-first-out + * (LIFO), element priority, and arbitrary. The remove() and + * poll() methods differ only in their behavior when the + * queue is empty: the remove() method throws an exception, + * while the poll() method returns null. * *
The {@link #element()} and {@link #peek()} methods return but do * not delete the element that would be obtained by a call to @@ -41,11 +46,13 @@ package java.util; * defined in the {@link java.util.concurrent.BlockingQueue} interface, which * extends this interface. * - *
Queue implementations generally do not allow insertion of - * null elements. Even in the few implementations that permit it, - * it is a bad idea, as null is also used as a special return value - * by the poll method to indicate that the queue contains no - * elements. + *
Queue implementations generally do not allow insertion + * of null elements, although some implementations, such as + * {@link LinkedList}, do not prohibit insertion of null. + * Even in the implementations that permit it, null should + * not be inserted into a Queue, as null is also + * used as a special return value by the poll method to + * indicate that the queue contains no elements. * *