Collecting Objects - Beginning Java 7 - page 483

As Table5-6 reveals, Deque declaresmethodstoaccesselementsatbothendsofthe
deque.Methodsareprovidedtoinsert,remove,andexaminetheelement.Eachofthese
methodsexistsintwoforms:onethrowsanexceptionwhentheoperationfails,theother
returnsaspecialvalue(eithernullorfalse,dependingontheoperation).Thelatterform
of the insert operation is designed specifically for use with capacity-restricted Deque
implementations; in most implementations, insert operations cannot fail.
Figure5-2 revealsatablefrom Deque 'sJavadocumentationthatnicelysummarizes
both forms of the insert, remove, and examine methods for both the head and the tail.
Figure 5-2. Deque declares twelve methods for inserting, removing, and examining
elements at the head or tail of a deque.