Abstract Data Types

Data Design and Implementation Abstract Data Types

Definitions of Java TYPES Atomic or primitive type A data type whose elements are single, non-decomposable data items - e.g, an int or a float variable Composite type : A data type whose elements are composed of multiple data items e.g. A CLASS

Structured composite type • Structured composite type: • An organized collection of components . The organization determines how to access the components of the collection • E.g. An Array or A Tree

Atomic (Simple) and Composite Data Types

Java’s Built-In Types

The Java Class Construct • is used to create composite, unstructured data types. • It is composed of : • 1. named data fields ( instance variables) 2. methods.

An array differs from a class : • An array is ahomogenous structure, whereas classes are heterogeneous structures. E.g. an array of integers has only integers in it. A class has variables of different types and methods

Accessing components • A component of an array is accessed by its position in the array e.g. board[2] [3]

Arrays • Because array components are accessed by position, • an array is a structured composite type.

Component of square: • A component of a class is accessed by an identifier (the object created of it). • Square sq = new Square(10,20, 40, Color.Red); • int x = sq.getX(); • We access the parts of the class with an object

Because class components are accessed by creating an object, • an class is a unstructured composite type.

Definitions Data abstraction: The separation of a data type’s logical properties from its implementation • A doctor sees (abstracts) the person as patient. E.g. name, height, weight of a person • An employer sees (abstracts) a person as Employee. E.g.name, age, health, degree of study, of a person.

Data encapsulation • We can abstract the important characteristics of Person • and store all the characteristics of a person in Person class • The Person class can be used by both the Doctor or Employer classes or ……..others

Abstract Data Type • An abstract data type is an interface • a) it defines a collection of data e.g. an array of clients • b)and the particular operations that are allowed on that array • ( through methods )

ABSTRACT DATA TYPES – ADT’ s • An ADT : • therefore has a name • E.G. A STACK, A QUEUE, An ARRAYLIST • A domain of values(data) - the elements in the stack, items stored in the array in the ArrayList • a set of operations that can be performed (methods) on the data

Collections- Details • A collection is an object that serves as a repository for other objects. • MOST ADT are Collections - since they store the data they are operating on • The Java Collections Framework contains classes that represent collections of objects.

Collections & ADT’s • In general, a collection refers to a class whose role is to: • provide methods to add, remove and • manage the elements that are in the collection.

Collections - ArrayList • The ArrayList classin the Collections Frameworkis implemented with an array. • There is also a SortedArrayList, which maintains the array in sorted order

Collections & ADT’s • Collections can be implemented in a variety of ways. • The ArrayListuses an Array and contains methodsthat perform operations on array. e.g.Adding or deleting items etc.

ADT’s • ADT’scan be implemented with both e.g. arrays or linked lists. • The choice of an array or a linked listdepends upon the implementation

The ArrayList Class • IS Part of the java.util package. • An ArrayList list can grow and shrinkdepending on need. • When the array is full, its size is doubled

ARRAYLIST • ArrayList class: you store variables of type Object. • Or now type T- a generic type built on class Object

ArrayList • An ArrayList has a size() method - how many objects it is currently holding • It has other methods : • add, remove, find , isEmpty etc. See: • http://docs.oracle.com/javase/6/docs/api/java/util/ArrayList.html

ArrayListOperations

Use Arraylist – unsorted - when: • The amount of space required may change from one execution of the program to the next. • The position of an element in the array list has no relevance to the application. • There is no order to the items stored

Collection Interface & Map Interface

LIST & SET INTERFACEs

public interface List<E> extends Collection<E> • { • E get(int index); • E set(int index, E element); • boolean add(E element); • void add(int index, E element); • E remove(int index); • boolean addAll(int index, Collection<? extends E> c); • int indexOf(Object o); • int lastIndexOf(Object o); • ListIterator<E> listIterator(); ListIterator<E> listIterator(int index); }

Collection Interface-List inherits these methods • public interface Collection<E> extends Iterable<E> { • int size(); • boolean isEmpty(); • boolean contains(Object element); • boolean add(E element); • boolean remove(Object element); • Iterator<E> iterator(); • boolean containsAll(Collection<?> c); • boolean addAll(Collection<? extends E> c); • boolean removeAll(Collection<?> c); • boolean retainAll(Collection<?> c); • void clear(); • public <T> T[] toArray(T[] a);

Designing ADTs this term • Determine the general purpose of your program. • List the specific types of operations the application program performs.

DESIGNING AN ADT • Decide first which ADT to use: • an ArrayList , A Stack? Depends on the problem • Identify a set of public methods to be provided by the ADT class to perform the desired operations

Designing ADTs • Identify potential error situations and classify into • Those that are handled by throwing an exception • Those that are ignored.

Designing ADTs • Define the needed exception classes. • Decide on a protection level for the identified data. • Implement the ADT. ( Using the ARRAYLIST OR STACK • Create a test driver and test your ADT.

Analysis of List Implementations • In both array and linked implementations, • many operations are similar in efficiency • Most are O(1), • except when shifting or searching occurs, in which case they are order O(n) 35

Abstract Data Types