CollectionFramework In core Java

Session 3 - Exception-Handling Java Programming

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Collection Framework(java.util Package)


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Framework (in software):a general system of components for architectural solutions.

Collection:any collection of Objects


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Overview (contd) Collection, Iterator Lists, ListIteratorListArrayListLinkedList

Stack Queue,

PriorityQueue

SetsSetTreeSetHashSet

MapsMapTreeMapHashMap

All the interfaces and classes are part of the java.util package.


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Overview (contd)

interfaceCollection

interfaceIterator

interfaceComparable

interfaceComparator

interfaceQueue

interfaceMap

Stack PriorityQueue

HashMapTreeMap

LinkedListArrayList TreeSet HashSet

interfaceList

interfaceSet

interfaceListIterator

CollectionSet

TreeSetHashSet

ListArrayList

LinkedList

TreeSetTreeMap

PriorityQueue


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Holds references to objects Can contain references to two

equal objects.(a.equals (b)) An object can change while in a

collection (unless it is immutable).


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Overview (contd)CollectionListStackSet

A map takes two object type parameters:Map

Because collections work with different types, these are called generic collections or generics


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Collection, Iterator Collection interface

represents any collection. A collection has its own

iterator(s).(returned iterator method);The traversal sequencedepends on the collection.

interfaceCollection

interfaceIterator


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Collection Methods

boolean isEmpty ()int size ()boolean contains (Object obj)boolean add (E obj)boolean remove (E obj)Iterator iterator ()

Supplies an iterator for this collection

interfaceCollection

interfaceIterator


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Iterator Methods

boolean hasNext ()E next ()void remove ()

What is next is determined

Removes the last visited element

interfaceCollection

interfaceIterator


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Iterator For Each Loop

Iterator iter =words.iterator();

while (iter.hasNext ()){String word = iter.next ();

< ... process word > }

Collection words = new ArrayList();



Lists, ListIterator In a list all elements are numbered

a0, a1, ..., an-1 java.util:List interfaceArrayListLinkedList

ListIterator is an extended iterator, (subinterface of Iterator)



Lists (contd)

interfaceCollectioninterfaceIterator


ArrayList LinkedList

interfaceSet

interfaceList



E get (int i)E set (int i, E obj)void add (int i, E obj)E remove (int i)int indexOf (Object obj)ListIterator listIterator ()

ListIterator listIterator (int i)

List Methods interfaceCollectioninterfaceIterator


interfaceList

Returns a ListIterator that starts iterations at index i



ListIterator Methodsint nextIndex ()

boolean hasPrevious ()E previous ()int previousIndex ()void add (E obj)void set (E obj)

Can traverse the list backward

(inserts after the last visited element)

Can change elements (changes the last visited element)



ArrayList Represents a list as adynamic array Provides random access to the

elements Implements all the methods of

List

interfaceList


...



LinkedList

Doubly-linked list with a header node.

Implements the methods of List

a0 a1 a2 an-1...

header

interfaceList




LinkedList (contd)

Additional methods

interfaceList


void addFirst (E obj)void addLast (E obj)E getFirst ()E getLast ()E removeFirst ()E removeLast ()



ArrayList vs. LinkedList Implements

array+Provides

random access- Insert, removing

elements shifts elements

- Needs to be resized

Implements list -No random access

+Insert, removing elements is done by rearranging the links

+Nodes are dynamically added



ArrayList vs. LinkedList (contd)

for (int i = 0; i < list.size(); i++){

Object x = list.get (i);...

}

Iterator iter = list.iterator ( );while (iter.hasNext ( )){

Object x = iter.next ( );...

}

for (Object x : list){

...}



Stacks

Provides temporary storage LIFO (Last-In-First-Out) manner.

Useful in nested structuresmethods calling other methods

push and pop. Implemented as java.util.Stack

class



Stacks (contd)

Stack



Stack Methods

boolean isEmpty ()E push (E obj)E pop ()E peek ()

Returns obj; use as void

Returns the top element without removing it from the stack



Queues Provides temporary storage in

the FIFO manner. Useful in events that have to be

processed in order of their arrival

java.util:Queue interfaceLinkedList (implements Queue)



Queues (contd)

LinkedList

interfaceQueue



QueueMethods

LinkedList

interfaceQueue

boolean isEmpty ()boolean add (E obj)E remove ()E peek () Returns the first element

without removing it from the queue



Queues (contd)

Queue q =new LinkedList ();

Methods added to LinkedList to implement Queue interface:

add == addLastremove== removeFirstpeek == getFirst



Priority Queues

In a priority queue, items are processed NOT in order of arrival, but in order of priority.

java.util:Queue interfacePriorityQueue (implements Queue)



PriorityQueue

interfaceQueue

Priority Queues (contd)

The same methods as in Queue: isEmpty, add, remove, peek.



Sets A set is without duplicate values Designed for finding a value

quickly java.util:Set interfaceTreeSetHashSet



Sets (contd)interfaceCollection

TreeSet HashSet

interfaceSet



TreeSet

Works with Comparableobjects

contains, add, and removemethods

Iterator returns elements in ascending order

TreeSet HashSet

interfaceSet



HashSet

Works with objects for which reasonable hashCode and equals methods are defined

contains, add, and removemethods

Iterator returns elements in no particular order

TreeSet HashSet

interfaceSet



Maps

It represents a correspondence between a set of keys , values

Only one value can correspond to a given key;

several keys can be mapped onto the same value

keys values



Maps (contd)

TreeMap HashMap

interfaceMap



Map Methods

TreeMap HashMap

interfaceMap

boolean isEmpty ()int size ()V get (K key)V put (K key, V value)V remove (K key)Set keySet ()



TreeMap

Works with Comparable keys containsKey, get, and put

methods

TreeMap HashSet

interfaceMap



HashMap

Works with keys for which reasonable hashCode and equalsmethods are defined

containsKey, get, and put methods

TreeMap HashMap

interfaceMap



Example: traversing all key-value pairsimport java.util.*;

Map AuctionItems =new TreeMap ();

AuctionItems.put (1, ARTPEICE);...for (Integer key : AuctionItems.keySet() ){ String name = AuctionItems.get (key);

System.out.println (key + " : " + name);}



Review: Why Java collections are called generic? Name several methods of Collection. What is an iterator? How can we obtain an iterator for a given

collection? Guess what happens when we call iter.next()

when there is no next element.



Review (contd): What are the properties of a list? Name the key methods of the List interface. How is ArrayList implemented? How is LinkedList implemented?



Case Study: Stock Exchange

Implements a Suryodaya stock exchange

Uses TreeSet, TreeMap, HashMap, Queue, and PriorityQueue classes

A chance to practice structural and object-oriented design



Stock Market Basics Stocks are listed on a stock exchange, such

as Suryodaya Stock Exchange. A particular stock is identified by its trading

symbol (for example, SUNW for Sun Microsystems or MSFT for Microsoft)

Stocks are usually traded in multiples of 100 Stock prices are in Rs. Online brokerage firms allow customers to

trade stocks online from their computers



Stock Market Terms Buy order an order to buy shares of stock Sell order an order to sell shares of stock Limit order specifies the maximum price for

a buy or a minimum price for a sell Ask asking price for a sell order Bid offer to buy at a certain price Market order an order to buy or sell at the

market price (the lowest ask or the highest bid, respectively)



SafeTrade Program Registered users trade shares. A user must login first. The program can register a new user. A logged in user can place buy and sell orders

and get price quotes for stocks. Users receive messages when their orders are

executed



SafeTrade Program (contd) Runs on a single computer; each active user

opens a separate trading window. Does not keep track of cash or of the number

of shares available on each users account.



SafeTrade Program (contd)



SafeTrade Program Design

Structural Design

OODesign

Detailed Design

Classes and objects

Data structures used

Fields, constructors, and methods



SafeTrade Structural Design

Queue => PriorityQueue

(with descending price comparator)

Buy orders for each stock

Queue => PriorityQueue

(with ascending price comparator)

Sell orders for each stock

Map => HashMapListed stocks

Queue => LinkedListMailbox for each trader

Set => TreeSetLogged-in tradersMap => TreeMapRegistered traders

interface => classData



Structural Design Tradeoffs

Registered users: large number (100,000s) access time is not critical

Binary Search

Tree (TreeMap)

Listed stocks: relatively small number fast access time is critical



SafeTrade OO Design

SafeTrade

StockExchange Brokerage

TraderWindow

Trader Stock

PriceComparator TradeOrder

LoginWindow

interface Login

StockExchange Brokerage Stock Trader TraderWindow PriceComparator



Part 1: Trader registration and login

SafeTrade LoginWindow

interfaceLogin



Part 2: Stocks and ordersTraderWindow

CollectionFramework In core Java

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