Queues, Deques, and Priority Queues - Data Structures and Abstractions with Java - page 260

public T removeLast()
Retrieves and removes the entry at the back of this deque, but throws NoSuchElementException
if the deque is empty prior to the operation.

public T pollLast()
Retrieves and removes the entry at the back of this deque, but returns null if the deque is
empty prior to the operation.

public T getFirst()
Retrieves the entry at the front of this deque, but throws NoSuchElementException if the
deque is empty.

public T peekFirst()
Retrieves the entry at the front of this deque, but returns null if the deque is empty.

public T getLast()
Retrieves the entry at the back of this deque, but throws NoSuchElementException if the
deque is empty.

public T peekLast()
Retrieves the entry at the back of this deque, but returns null if the deque is empty.

public boolean isEmpty()
Detects whether this deque is empty.

public void clear()
Removes all entries from this deque.

public int size()
Gets the number of entries currently in this deque.

The interface Deque extends the interface Queue , so it also has the methods add , offer , remove ,
poll , element , and peek that were described earlier in Segment 10.13. In addition, Deque declares
the following two stack methods:

public void push(T newEntry)
public T pop()

These methods are like the ones defined in the class java.util.Stack , which we encountered ear-
lier in Segment 5.23 of Chapter 5, except that push is a void method in Deque . As we mentioned in
Chapter 5, you should no longer use the standard class Stack . The following segment describes an
alternate class for you to use.
The online documentation for the interface Deque , as given at download.oracle.com/javase/7/
docs/api , tabulates the correspondence between deque methods and both queue and stack methods.

Java Class Library: The Class ArrayDeque
10.18

The standard package java.util in the Java Class Library contains the class ArrayDeque , which
implements the interface Deque that we just described. Since Deque declares methods appropriate for a
deque, a queue, and a stack, you can use ArrayDeque to create instances of any of these data collections.