Data structure lecture

Data Structures Data Structures Chapter Contents Chapter Contents Chapter Objectives 12.1 Introductory Example: Counting Internet Addresses 12.2 The ArrayList and LinkedList Classes 12.3 Example: A Stack Application and Class 12.4 Example: A Queue Class 12.5 An Introduction to Trees Part of the Picture: Data Structures 12.6 Graphical/Internet Java: A PolygonSketcher Class Chapter Objectives Chapter Objectives  Study the Java collection classes, ArrayList and LinkedList  Show how to build collection classes  Study the stack and queue structures  Learn about linked structures  linked lists and binary trees  Implement and use linked structures  Discover how collection classes are used in graphical programming Review Arrays Review Arrays  An array stores a sequence of values type [] anArray = new type [ capacity ];  Drawback: – capacity of array fixed – must know max number of values at compile time – either the program runs out of space or wastes space  Solution: collection classes – capacity can grow and shrink as program runs 12.1 Introductory Example: 12.1 Introductory Example: Counting Internet Addresses Counting Internet Addresses  Internet TCP/IP addresses provide for two names for each computer – A host name, meaningful to humans – an IP address, meaningful to computers  Problem: – network administrator needs to review file of IP addresses using a network gateway  Solution: – read file of addresses – keep track of addresses and how many times each address shows up in the file Class Class AddressCounter AddressCounter  Note source code, Figure 12.1  Attributes – maximum message length – address – count  Methods – constructor – comparison method, equals() – count incrementer – accessors for address, count – to-string converter for output Class Class GatewayUsageCounter GatewayUsageCounter  Note source code, Figure 12.2  Purpose – counts IP addresses using an array list  Receives name of text file from args[0]  Action: – reads IP address from file – prints listing of IP addresses and access count for each  Note use of ArrayList class – can grow or shrink as needed 12.2 The 12.2 The ArrayList ArrayList and and LinkedList LinkedList Classes Classes  Collection classes provide capability to grow and shrink as needed  Categories of collection classes – Lists: store collection of items, some of which may be the same – Sets: store collection of items with no duplicates – Maps: store collections of pairs, each associates a key with an object  Note List methods, table 12.1 ArrayList ArrayList Class Class  Implements the List using an array – by using an Object array, can store any reference type – cannot directly store primitive types – can indirectly store such values by using instances of their wrapper types  Consider the declaration: ArrayList addressSequence = newArrayList(); AddressSeqeunce size array 0  Adding to Adding to addressSequence addressSequence  The command addressSequence.add(anAddressCounter); – appends anAddressCounter object to the sequence  The system will then … AddressSeqeunce size array 0 [0] [1] [2] . . . [m-1] 128.159.4.201 Allocate the array Make first element point to the AddressCounter 1 Update size attribute of the ArrayList [...]... can be added only at back of ArrayList – to insert a value and "shift" others after it requires extensive copying of values – similarly, deleting a value requires shifting  We need a slightly different structure to allow simple insertions and deletions – the LinkedList class will accomplish this The LinkedList Class  Given LinkedList alist = new LinkedList(); aList.add(new(integer(88)); aList.add(new(integer(77));... list Variations on Linked Lists  Lists can be linked doubly as shown  Lists can also be linked in one direction only – attribute would not need link to tail – node needs forward link and pointer to data only – last item in list has link set to null  Lists can be circularly linked – last node has link to first node Using a LinkedList  Solve the IP address counter to use LinkedList  Note source... addressSequence head  size tail 0  Adding to the Linked List  Results of command for first add addressSequence.add(anAddressCounter); addressSequence head size tail 0 •Successive adds • create more nodes and data values •adjust links   123.111.345.444, 1 Accessing Values in a Linked List  Must use the get method ((AddressCounter) addresssSequence.get(index)).incrementCount();  A LinkedList has no array... addressSequence.add(n, new anAddressCounter); Which will … – build a new node – update head and tail links if required – update node handle links to place new node to be nth item in the list – allocates memory for the data item Choosing the Proper List Algorithm Efficiency  "Time-efficiency" is not a real-time issue – rather an issue of how many steps an algorithm requires  Linear time – time proportional to n – referred... "order n"  Constant time – expressed as O(1) Demonstration of Efficiency  Note sample program ListTimer, Figure 12.4, demonstrates performance  Observations – appending to either ArrayList or LinkedList structures takes negligible time – far more time-consuming to access middle value in a LinkedList than an ArrayList – far more time consuming to insert values into an ArrayList than a LinkedList Conclusions... choice  Implement as an ArrayList attribute – poor choice – adding values at one end, removing at other end require multiple shifts Implementing a Queue Class  Build a Queue from scratch – build a linked structure to store the queue elements  Attributes required – handle for the head node – handle for tail node – integer to store number of values in the queue – use SinglyLinkedNode class, source code, . Data Structures Data Structures Chapter Contents Chapter Contents Chapter Objectives 12.1 Introductory Example:. collection classes  Study the stack and queue structures  Learn about linked structures  linked lists and binary trees  Implement and use linked structures  Discover how collection classes. Application and Class 12.4 Example: A Queue Class 12.5 An Introduction to Trees Part of the Picture: Data Structures 12.6 Graphical/Internet Java: A PolygonSketcher Class Chapter Objectives Chapter