abstraction the word abstract means "considered apart from detailed specifications or implementation an abstraction is the essence or important characteristics of something the office of presidentfor exampleis an abstractionconsidered apart from the individual who happens to occupy that office the powers and responsibilities of the office remain the samewhile individual office-holders come and go in object-oriented programmingthenan abstract data type is class considered without regard to its implementation it' description of the data in the class (fields) list of operations (methodsthat can be carried out on that dataand instructions on how to use these operations specifically excluded are the details of how the methods carry out their tasks as class useryou're told what methods to callhow to call themand the results you can expectbut not how they work the meaning of abstract data type is further extended when it' applied to data structures such as stacks and queues as with any classit means the data and the operations that can be performed on itbut in this context even the fundamentals of how the data is stored become invisible to the user users not only don' know how the methods workthey also don' know what structure is used to store the data for the stackthe user knows that push(and pop((and perhaps few other methodsexist and how they work the user doesn' (at least not usuallyneed to know how push(and pop(workor whether data is stored in an arraya linked listor some other data structure like tree the interface an adt specification is often called an interface it' what the class user sees--usually its public methods in stack classpush(and pop(and similar methods form the interface adt lists now that we know what an abstract data type iswe can mention another onethe list list (sometimes called linear listis group of items arranged in linear order that isthey're lined up in certain waylike beads on string or houses on street lists support certain fundamental operations you can insert an itemdelete an itemand usually read an item from specified location (the third itemsaydon' confuse the adt list with the linked list we've been discussing in this list is defined by its interfacethe specific methods used to interact with it this interface can be implemented by various structuresincluding arrays and linked lists the list is an abstraction of such data structures