Abstract Data Types Linked Lists Abstract Data TypeADT

Abstract Data Types Linked Lists

Abstract Data Type(ADT) n n 4 ADT--a specification, in abstract terms only, without reference to programming language or machine dependent terminology. ADT--contains two parts: description of the data together with any internal structure that thedata has description of the valid operations that can be performed on this data

ADT n n 2 Because abstract--can not be used directly in a program, but can be implemented into concrete instances, which can be used in programs To insure conditions that will lead to successful application, ADT should make use of the exception mechanism

Ideal properties for ADT List structure n n 4 should occupy exactly as much memory as necessary should be able to grow at any time, and accomplish growth quickly should be able to shrink at any time and return unused memory to the JVM should be ordered so that every element has a well-defined location.

ADT List--definition n n 2 List--an ordered structure of elements such that it is either empty or has a unique first element, every element except for the last one has one immediate successor, and the last element is that one without a successor. One element in a non-empty List is always designated as the current element.

ADT List--operations n n 4 Create an empty List Designate the first element of a nonempty List as the current element Move the current element to the successor of the current element in a non-empty List, unless the current element is last Insert an element into the List

ADT List--operations (cont. ) n n n Retrieve the element designated as current, unless the List is empty Remove the element designated as current, unless the List is empty Replace the element designated as current, by another element unless the List is empty Check if current element is last 5

List class--definition n 3 A List is either an empty or sequential structure of elements such that one element is always designated as current List supports the following methods: constructor: creates an empty List containing no elements public void first(): make first element current, can only be used on a nonempty List

List class--definition (cont. ) n n n 3 Public void next(): makes the element after the current one the (new) current one public void insert (Object o): inserts an element, or object, into the List public Object retrieve(): returns current element , can only be used on a nonempty List

List class--definition (cont. ) n n 4 public void remove (): deletes current element from the List, only on nonempty public void replace (Object o): replaces current element by another one, can only be used on a nonempty List public boolean is. Empty(): true if List empty, false otherwise public boolean is. Last(): true if element last, false otherwise

Node n n n 3 A utility class used to create lists and other list-like sequential structures Need inside a List--a smart obect that can store data and knows who its immediate successor, if any, is Hence, Node has two pieces: one piece to store a Java object, and another piece to store a reference to another Node

Node (cont. ) n n n 3 A node can return and replace the Object stored A node can contain a reference to another node called the successor Implementation: a node can contain two non-private fields, one called data that stores the actual object and another called next that stores either a reference to another node or “null”.

Node n n GO TO node code. Draw on board 2

Circular node n n n n (put picture on board) Node A = new Node(); Node B = new Node(); Node C = new Node(); A. next=B; B. next=C; C. next=A;