1. 1 COS 260 DAY 9 Tony Gauvin

2. 2 Agenda Questions? 3 rd Mini quiz –Good results ->All A’s –Threw out question on name overloading 4 th Mini quiz next class –Chapter 4 Assignment 2 posted –Due Oct 5 prior to class (next Monday) Capstone Discussion –Capstone Project Description Fall 2015.pdfCapstone Project Description Fall 2015.pdf Finish Discussion on Grouping objects Begin Discussion on More Sophisticated Behaviors

3. 3 Overloading Name overloading –this.name = name; Method overloading –this.name() = name(); Operator overloading – 3 + 4 –3.0 + 4.0 –“3” + “4” Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

4. Grouping objects Introduction to collections 5.0

5. 5 Review Collections allow an arbitrary number of objects to be stored. Class libraries usually contain tried- and-tested collection classes. Java’s class libraries are called packages. We have used the ArrayList class from the java.util package. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

6. 6 ArrayList Review Items may be added and removed. Each item has an index. Index values may change if items are removed (or further items added). The main ArrayList methods are add, get, remove and size. ArrayList is a parameterized or generic type. –Can store any object type Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

7. 7 Review Loop statements allow a block of statements to be repeated. The for-each loop allows iteration over a whole collection. for (ElementType element : collection) { do stuff } Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

8. 8 Review Loop statements allow a block of statements to be repeated. The for-each loop allows iteration over a whole collection. The while loop allows the repetition to be controlled by a boolean expression. All collection classes provide special Iterator objects that provide sequential access to a whole collection. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

9. 9 The auction project The auction project provides further illustration of collections and iteration. Examples of using null. Anonymous objects. Chaining method calls. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

10. 10 The auction project

11. 11 null Used with object types. Used to indicate, 'no object'. We can test if an object variable holds the null value: if(highestBid == null) … Used to indicate ‘no bid yet’.

12. 12 Anonymous objects Objects are often created and handed on elsewhere immediately: Lot furtherLot = new Lot(…); lots.add(furtherLot); We don’t really need furtherLot : lots.add(new Lot(…));

13. 13 Chaining method calls Methods often return objects. We often immediately call a method on the returned object. Bid bid = lot.getHighestBid(); Person bidder = bid.getBidder(); We can use the anonymous object concept and chain method calls: lot.getHighestBid().getBidder()

14. 14 Chaining method calls String name = lot.getHighestBid().getBidder().getName(); Each method in the chain is called on the object returned from the previous method call in the chain. Returns a Bid object from the Lot Returns a Person object from the Bid Returns a String object from the Person

15. Grouping objects Arrays (fixed size collection)

16. 16 Fixed-size collections Sometimes the maximum collection size can be pre-determined. A special fixed-size collection type is available: an array. Unlike the flexible List collections, arrays can store object references or primitive-type values. (generic collections can only store object references) Arrays use a special syntax. [ ] Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

17. 17 The weblog-analyzer project Web server records details of each access. Supports analysis tasks: –Most popular pages. –Busiest periods. –How much data is being delivered. –Broken references. Analyze accesses by hour. u_ex150930.log Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

18. 18 Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

19. 19 Creating an array object Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling public class LogAnalyzer { private int[] hourCounts; private LogfileReader reader; public LogAnalyzer() { hourCounts = new int[24]; reader = new LogfileReader(); }... } Array object creation — specifies size Array variable declaration — does not contain size

20. 20 The hourCounts array Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

21. 21 Using an array Square-bracket notation is used to access an array element: hourCounts[...] Elements are used like ordinary variables. The target of an assignment: hourCounts[hour] =...; In an expression: hourCounts[hour]++; adjusted = hourCounts[hour] – 3; Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

22. 22 Standard array use Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling private int[] hourCounts; private String[] names;... hourCounts = new int[24];... hourcounts[i] = 0; hourcounts[i]++; System.out.println(hourcounts[i]); declaration creation use

23. 23 Array literals Array literals in this form can only be used in declarations. Related uses require new : Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling private int[] numbers = { 3, 15, 4, 5 }; declaration, creation and initialization numbers = new int[] { 3, 15, 4, 5 }; The size is inferred from the data.

24. 24 Array length NB: length is a field rather than a method! It cannot be changed – ‘fixed size’. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling private int[] numbers = { 3, 15, 4, 5 }; int n = numbers.length; no brackets!

25. 25 The for loop There are two variations of the for loop, for-each and for. The for loop is often used to iterate a fixed number of times. Often used with a variable that changes a fixed amount on each iteration. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

26. 26 For loop pseudo-code Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling for(initialization; condition; post-body action) { statements to be repeated } General form of the for loop Equivalent in while-loop form initialization; while(condition) { statements to be repeated post-body action }

27. 27 A Java example Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling for(int hour = 0; hour < hourCounts.length; hour++) { System.out.println(hour + ": " + hourCounts[hour]); } int hour = 0; while(hour < hourCounts.length) { System.out.println(hour + ": " + hourCounts[hour]); hour++; } for loop version while loop version

28. 28 Practice Given an array of numbers, print out all the numbers in the array, using a for loop. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling int[] numbers = { 4, 1, 22, 9, 14, 3, 9}; for...

29. 29 Practice Fill an array with the Fibonacci sequence. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling int[] fib = new int[100]; fib[0] = 0; fib[1] = 1; for... 0 1 1 2 3 5 8 13 21 34...

30. 30 for loop with bigger step Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling // Print multiples of 3 that are below 40. for(int num = 3; num < 40; num = num + 3) { System.out.println(num); }

31. 31 Review Arrays are appropriate where a fixed- size collection is required. Arrays use a special syntax. For loops are used when an index variable is required. For loops offer an alternative to while loops when the number of repetitions is known. Used with a regular step size. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

32. 32 Chapter Terms Collections Array Iterator For-each For While index Import statement Library Package Anonymous object Definite Iteration Indefinite Iteration Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

33. More sophisticated behavior Using library classes to implement some more advanced functionality 5.0

34. 34 Main concepts to be covered Using library classes Reading documentation Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

35. 35 The Java class library Thousands of classes. Tens of thousands of methods. Many useful classes that make life much easier. Library classes are often inter- related. Arranged into packages. https://docs.oracle.com/javase/8/docs/api/ Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

36. 36 Working with the library A competent Java programmer must be able to work with the libraries. You should: know some important classes by name; know how to find out about other classes. Remember: we only need to know the interface, not the implementation. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

37. 37 A Technical Support System A textual, interactive dialog system Idea based on ‘Eliza’ by Joseph Weizenbaum (MIT, 1960s) –http://www.masswerk.at/elizabot/http://www.masswerk.at/elizabot/ Explore tech-support-complete … Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

38. 38 Main loop structure boolean finished = false; while(!finished) { do something if(exit condition) { finished = true; } else { do something more } Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling A common iteration pattern.

39. 39 Main loop body String input = reader.getInput();... String response = responder.generateResponse(); System.out.println(response); Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

40. 40 The exit condition String input = reader.getInput(); if(input.startsWith("bye")) { finished = true; } Where does ‘ startsWith ’ come from? What is it? What does it do? How can we find out? Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

41. 41 Reading class documentation Documentation of the Java libraries in HTML format; Readable in a web browser Class API: Application Programmers’ Interface Interface description for all library classes Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

42. 42 Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

43. 43 Interface vs implementation The documentation includes the name of the class; a general description of the class; a list of constructors and methods return values and parameters for constructors and methods a description of the purpose of each constructor and method the interface of the class Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

44. 44 Interface vs implementation The documentation does not include private fields (most fields are private) private methods the bodies (source code) of methods the implementation of the class Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

45. 45 Documentation for startsWith startsWith –public boolean startsWith(String prefix)String Tests if this string starts with the specified prefix. Parameters: –prefix - the prefix. Returns: –true if the …; false otherwise Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

46. 46 Methods from String contains endsWith indexOf substring toUpperCase trim Beware: strings are immutable! Cannot be changed! Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

47. 47 Using library classes Classes organized into packages. Classes from the library must be imported using an import statement (except classes from the java.lang package). They can then be used like classes from the current project. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

48. 48 Fixing the Support System termination input Trim input –“bye” vs. “ bye ” Handle change in case –“Bye” vs “bye” Check for equality instead of “startsWith” Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

49. 49 Packages and import Single classes may be imported: import java.util.ArrayList; Whole packages can be imported: import java.util.*; Importation does not involve source code insertion. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

50. 50 Using Random (need for games) The library class Random can be used to generate random numbers (look up in documentation) Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling import java.util.Random;... Random rand = new Random();... int num = rand.nextInt(); int value = 1 + rand.nextInt(100); int index = rand.nextInt(list.size()); random-check.zip

51. 51 Selecting random responses for TechSupport Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling public Responder() { randomGenerator = new Random(); responses = new ArrayList (); fillResponses(); } public void fillResponses() { fill responses with a selection of response strings } public String generateResponse() { int index = randomGenerator.nextInt(responses.size()); return responses.get(index); }

52. 52 Parameterized classes The documentation includes provision for a type parameter: –ArrayList These type names reappear in the parameters and return types: –E get(int index) –boolean add(E e) Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

53. 53 Parameterized classes The types in the documentation are placeholders for the types we use in practice: –An ArrayList actually has methods: –TicketMachine get(int index) –boolean add(TicketMachine e) –Replace “E” with the type you will use Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

54. 54 Review Java has an extensive class library. A good programmer must be familiar with the library. The documentation tells us what we need to know to use a class (its interface). Some classes are parameterized with additional types. Parameterized classes are also known as generic classes or generic types. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

55. More sophisticated behavior Using library classes to implement some more advanced functionality

56. 56 Main concepts to be covered Further library classes Set Map Writing documentation javadoc Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

57. 57 Using sets import java.util.HashSet;... HashSet mySet = new HashSet (); mySet.add("one"); mySet.add("two"); mySet.add("three"); for(String element : mySet) { do something with element } Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling Compare with code for an ArrayList !

58. 58 Tokenising Strings public HashSet getInput() { System.out.print("> "); String inputLine = reader.nextLine().trim().toLowerCase(); String[] wordArray = inputLine.split(" "); HashSet words = new HashSet (); for(String word : wordArray) { words.add(word); } return words; } Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

59. 59 Maps Maps are collections that contain pairs of values. Pairs consist of a key and a value. Lookup works by supplying a key, and retrieving a value. Example: a telephone book. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

60. 60 Using maps A map with strings as keys and values Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling "Charles Nguyen" :HashMap "(531) 9392 4587" "Lisa Jones""(402) 4536 4674" "William H. Smith""(998) 5488 0123"

61. 61 Using maps HashMap phoneBook = new HashMap (); phoneBook.put("Charles Nguyen", "(531) 9392 4587"); phoneBook.put("Lisa Jones", "(402) 4536 4674"); phoneBook.put("William H. Smith", "(998) 5488 0123"); String phoneNumber = phoneBook.get("Lisa Jones"); System.out.println(phoneNumber); Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

62. 62 List, Map and Set Alternative ways to group objects. Varying implementations available: –ArrayList, LinkedList –HashSet, TreeSet But HashMap is unrelated to HashSet, despite similar names. The second word reveals organizational relatedness. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

63. 63 Writing class documentation Your own classes should be documented the same way library classes are. Other people should be able to use your class without reading the implementation. Make your class a potential 'library class'! Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

64. 64 Elements of documentation Documentation for a class should include: the class name a comment describing the overall purpose and characteristics of the class a version number the authors’ names documentation for each constructor and each method Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

65. 65 Elements of documentation The documentation for each constructor and method should include: the name of the method the return type the parameter names and types a description of the purpose and function of the method a description of each parameter a description of the value returned Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

66. 66 javadoc Class comment: /** * The Responder class represents a response * generator object. It is used to generate an * automatic response. * * @author Michael Kölling and David J. Barnes * @version 1.0 (2011.07.31) */ Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

67. 67 javadoc Method comment: /** * Read a line of text from standard input (the text * terminal), and return it as a set of words. * * @param prompt A prompt to print to screen. * @return A set of Strings, where each String is * one of the words typed by the user */ public HashSet getInput(String prompt) {... } Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

68. 68 Public vs private Public elements are accessible to objects of other classes: Fields, constructors and methods Fields should not be public. Private elements are accessible only to objects of the same class. Only methods that are intended for other classes should be public. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

69. 69 Information hiding Data belonging to one object is hidden from other objects. Know what an object can do, not how it does it. Information hiding increases the level of independence. Independence of modules is important for large systems and maintenance. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

70. 70 Code completion The BlueJ editor supports lookup of methods. Use Ctrl-space after a method-call dot to bring up a list of available methods. Use Return to select a highlighted method. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

71. 71 Code completion in BlueJ Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

72. 72 Review Java has an extensive class library. A good programmer must be familiar with the library. The documentation tells us what we need to know to use a class (interface). The implementation is hidden (information hiding). We document our classes so that the interface can be read on its own (class comment, method comments). Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

73. Class and constant variables Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

74. 74 Class variables A class variable is shared between all instances of the class. In fact, it belongs to the class and exists independent of any instances. Designated by the static keyword. Public static variables are accessed via the class name; e.g.: –Thermometer.boilingPoint Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

75. 75 Class variables Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

76. 76 Constants A variable, once set, can have its value fixed. Designated by the final keyword. –final int max = list.size(); Final fields must be set in their declaration or the constructor. Combing static and final is common. Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

77. 77 Class constants static : class variable final : constant private static final int gravity = 3; Public visibility is less of an issue with final fields. Upper-case names often used for class constants: public static final int BOILING_POINT = 100; Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling