Data Structures and Abstract Data Types "Get your data structures correct first, and the rest of the...

Data Structures and Abstract Data Types

"Get your data structures correct first, and the rest of the program will write itself." - David Jones

Abstract Data Types Abstract Data Types (aka ADTs) are

descriptions of how a data type will work without implementation details

Description can be a formal, mathematical description

Java interfaces are a form of ADTs– some implementation details start to creep in

CS 221 - Computer Science II


Data Structures A Data Structure is:

– an implementation of an abstract data type and– "An organization of information, usually in

computer memory", for better algorithm efficiency."

aListList Object

size

myElements

5

A C E B A

0 1 2 3 4 5 6 7 8 9 10


Data Structure Concepts Data Structures are containers:

– they hold other data– arrays are a data structure– ... so are lists

Other types of data structures:– stack, queue, tree,

binary search tree, hash table,dictionary or map, set, and on and on

– en.wikipedia.org/wiki/List_of_data_structures

Different types of data structures are optimized for certain types of operations


Core Operations Data Structures have three core operations

– a way to add things– a way to remove things– a way to access things

Details of these operations depend on the data structure– Example: List, add at the end, access by

location, remove by location

More operations added depending on what data structure is designed to do

Implementing ADTs When implementing an ADT, the operations

and behaviors are already specified– think Java interface

But what use as the internal storage container for the concrete data type?– the internal storage container is used to hold the

items in the collection– initially slim pickings for choice of storage

containers: arrays anyone?– later add linked structures– now often an implementation of an ADT (which

use arrays or linked structures)CS 221 - Computer Science II

Bags and Sets Simplest ADT is a Bag

– items can be added, removed, accessed– no implied order to the items– duplicates allowed

Set– same as a bag, except duplicate elements not

allowed– union, intersection, difference, subset


Lists Items have a position in this Collection

– Random access or not?

Array Lists– internal storage container is native array

Linked Listspublic class Node{ private Object data;private Node next;

} firstlast


Stacks Collection with access only to the last

element inserted– Last in first out– push (insert)– pop (remove)– peek (top item)– make empty

TopData4

Data3

Data2

Data1


Queues Collection with access only to the item that

has been present the longest– first in,first out or last in, last out – enqueue (insert)– dequeue (remove) – front

Data4Data3Data2Data1

Front Back


Stacks and Queues in the Java Collection API

No queue in the Java collections ADT Stack extends Vector (which is almost

exactly like ArrayList)– Hmmm?

One reason the Java Collections Library is often said to be broken

no Queue in Collection API


Trees Similar to a linked listpublic class TreeNode{ private Object data;private TreeNode left;private TreeNode right;

} Root


Other Types of Trees Binary Search Trees

– sorted values

Heaps– sorted via a different algorithm

AVL and Red-Black Trees– binary search trees that stay balanced

Splay Trees B Trees


HashTables Take a key, apply function f(key) = hash value store data or object based on hash value Sorting O(N), access O(1) if a perfect hash

function and enough memory for table How deal with collisions?


Other ADTs Maps

– a.k.a. Dictionary– Collection of items with a key and associated

values– similar to hash tables, and hash tables often

used to implement Maps

Graphs– Nodes with unlimited connections between other

nodes

Sparse vectors and sparse matrices


Generic Containers ADTs or Collection classes should be

generic– only write them once, hold lots or all types of

data– Java achieves genericity through inheritance and

polymorphism

ADTs have an internal storage container– What is storing the stuff, – implementation vs. abstraction– in Java, usually holds Objects. Why?



ADTs and Data Structures in Programming Languages

Modern programming languages usually have a library of data structures– Java collections framework– C++ standard template library– .Net framework (small portion of VERY large

library)– Python lists and tuples– Lisp lists


Data Structures in Java Part of the Java Standard Library is the

Collections Framework– In class we will create our own data structures

and discuss the data structures that exist in Java

A library of data structures Built on two interfaces

– Collection– Iterator

http://java.sun.com/j2se/1.5.0/docs/guide/collections/index.html


The Java Collection Interface A generic collection Can hold any object data type Which type a particular collection will hold is

specified when declaring an instance of a class that implements the Collection interface

Helps guarantee type safety at compile time


Methods in the Collection interfacepublic interface Collection<E>{ public boolean add(E o)

public boolean addAll(Collection<? extends E> c)public void clear() public boolean contains(Object o) public boolean containsAll(Collection<?> c) public boolean equals(Object o)public int hashCode() public boolean isEmpty() public Iterator<E> iterator()public boolean remove(Object o) public boolean removeAll(Collection<?> c) public boolean retainAll(Collection<?> c)public int size() public Object[] toArray()public <T> T[] toArray(T[] a)

}


The Java ArrayList Class Implements the List interface and uses an

array as its internal storage container It is a list, not an array The array that actual stores the elements of

the list is hidden, not visible outside of the ArrayList class

All actions on ArrayList objects are via the methods

ArrayLists are generic. – They can hold objects of any type!


ArrayList's (Partial) Class Diagram

AbstractCollection

Object

AbstractList

ArrayList

Iterable

Collection

List

ArrayList Specification java.util Class ArrayList

java.lang.Object | +--java.util.AbstractCollection | +--java.util.AbstractList | +--java.util.ArrayList

All Implemented Interfaces: Cloneable, Collection, List, Serializable

void add(int index, Object element) Inserts the specified element at the specified position in this list.

boolean add(Object o) Appends the specified element to the end of this list.

void clear() Removes all of the elements from this list.

boolean contains(Object elem) Returns true if this list contains the specified element.

int indexOf(Object elem) Searches for the first occurence of the given argument, testing for equality using the equals method.

boolean isEmpty() Tests if this list has no elements.

Object set(int index, Object element) Replaces the element at the specified position in this list with the specified element.

int size() Returns the number of elements in this list.

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