This interface defines methods to access the elements at both ends of the deque. Methods are provided to insert, remove, and examine the element. Each of these methods exists in two forms: one throws an exception if the operation fails, the other returns a special value (either null or false, depending on the operation). The latter form of the insert operation is designed specifically for use with capacity-restrictedDeque implementations; in most implementations, insert operations cannot fail.
The twelve methods described above are summarized in the following table:
，力微休负重，言轻莫劝人。
