Stacks - Data Structures and Abstractions with Java - page 111

A BSTRACT D ATA T YPE : S TACK

D ATE

• A collection of objects in reverse chronological order and having the same data type

O PERATIONS

P SEUDOCODE UML D ESCRIPTION

push(newEntry) +push(newEntry: T): void

Task: Adds a new entry to the top of the
stack.
Input: newEntry is the new entry.
Output: None.

pop() +pop(): T

Task: Removes and returns the stack's top
entry.
Input: None.
Output: Returns either the stack's top entry
or, if the stack is empty before the
operation, null .

peek() +peek(): T

Task: Retrieves the stack's top entry without
changing the stack in any way.
Input: None.
Output: Returns either the stack's top entry
or, if the stack is empty, null .

isEmpty() +isEmpty(): boolean

Task: Detects whether the stack is empty.
Input: None.
Output: Returns true if the stack is empty.

clear() +clear(): void

Task: Removes all entries from the stack.
Input: None.
Output: None.

Note: Alternate names for methods
It is not unusual for a class designer to include aliases for certain methods. For example, you
could include the additional methods add and remove (or insert and delete ) in the ADT
stack to mean push and pop . Moreover, pull is sometimes used to mean pop , and getTop can
mean peek , so including them as aliases is reasonable.