1. An Introduction to Programming and Object Oriented Design using Java 2 nd Edition. May 2004 Jaime Niño Frederick Hosch Chapter 7 : Building a Text-based user interface.

2. 1May 2004Chapter 7 Objectives ñAfter studying this chapter you should understand the following: ñindependence of servers from clients; ñlikeliness of the user interface to change; ñi/o streams; ñstructure of a simple text-based user interface; ñpurpose and structure of a while loop; ñhow existing classes can be composed to define a new class.

3. 2May 2004Chapter 7 Objectives ñAlso, you should be able to: ñuse input/output objects to read and write data; ñbuild a simple text-based user interface; ñuse and trace a basic while statement; ñdefine classes whose implementations contain other classes as components.

4. 3May 2004Chapter 7 Relating User-interface and Model ñModel: objects that solve problem at hand. ñUser interface: interacts with user, getting input from user, and giving output to user, reporting on status of model. ñFlexibility in design: identifying these as separate subsystems.

5. 4May 2004Chapter 7 Stream-based I/O ñData streams: sequence of bytes. ñcharacter stream: sequence of characters ñ input stream: stream is a source of data for an application. ñoutput stream: stream is appliction destination (or sink).

6. 5May 2004Chapter 7 Standard Input and Output streams standard output: characters to display

7. 6May 2004Chapter 7 Writing standard output  System.out : provides methods for writing to standard output. public void println (String s) Write specified String to standard output and then terminate the line. public void print (String s) Write the specified String to standard output. public void println () Terminate current line by writing line terminator to standard output. public void flush () Flush stream: write buffered output to standard output and flush that stream.

8. 7May 2004Chapter 7 Input: nhUtilities.basicIO.BasicFileReader  Constructors : public BasicFileReader () Create a BasicFileReader attached to standard input. public BasicFileReader (String fileName) Create a BasicFileReader attached to the named file.

9. 8May 2004Chapter 7 Input: nhUtilities.basicIO.BasicFileReader  Command : public void readInt () Read a new int from input stream. The digit string is interpreted as a decimal integer. Characters following any white space in input stream must have format of an optionally signed decimal integer.

10. 9May 2004Chapter 7 readInt standard input 1 2 3 4 5 a b c  BasicFileReader lastInt =? Application standard input a b c  BasicFileReader lastInt =12345 Application before executing readInt() after executing readInt()

11. 10May 2004Chapter 7 Input: nhUtilities.basicIO.BasicFileReader ñQuery: public int lastInt () int most recently read by readInt. require: this.readInt() has been successfully performed.

12. 11May 2004Chapter 7 Input: nhUtilities.basicIO.BasicFileReader  readDouble and readWord skip white space at beginning of stream.  readDouble requires characters after white space have format of an optionally signed double literal.  readWord reads a sequence of nonwhite space characters. ñOther commands for reading from the input stream: public void readChar () Read a new character from this input stream. public void readDouble () Read a new double from this input stream. public void readLine () Read the rest of the line from this input stream. public void readWord () Read a new word from this input stream.

13. 12May 2004Chapter 7 Input: nhUtilities.basicIO.BasicFileReader ñOther queries: public char lastChar () Character most recently read by readChar. require: this.readChar() has been successfully performed. public double lastDouble () double most recently read by readDouble. require: this.readDouble() has been successfully performed. public String lastString () String most recently read by readWord or readLine. require: this.readWord() or this.readLine() has been successfully performed.

14. 13May 2004Chapter 7 Input: nhUtilities.basicIO.BasicFileReader ñOther queries: public boolean eof () End of input stream has been reached.

15. 14May 2004Chapter 7 Building an interface for Rectangle ñBuild an interface that let’s user specify dimensions of the Rectangle and ask for property to be displayed. class RectangleTUI A simple text-based interface for Rectangles. public RectangleTUI () Create a new RectangleTUI instance. public void start () Run the interface.

16. 15May 2004Chapter 7 Building an interface for Rectangle  Application creates interface and executes start : public class RectangleExample { public static void main (String[] argv) { (new RectangleTUI()).start(); }

17. 16May 2004Chapter 7 Building an interface for Rectangle ñInstance variables are initialized in constructor: ñRectangleTUI properties: private Rectangle rectangle; // the model private BasicFileReader in; //standard input public RectangleTUI () { this.rectangle = null; this.in = new BasicFileReader(); }

18. 17May 2004Chapter 7 Building an interface for Rectangle ñTo get Rectangle dimensions from user: private void createRectangle () Create a new Rectangle with user-provided dimensions. Uses readIntWithPrompt to get dimensions from user. private int readIntWithPrompt (String prompt) { System.out.print(prompt); System.out.flush(); in.readInt(); in.readLine(); return in.lastInt(); }

19. 18May 2004Chapter 7 Building an interface for Rectangle private void createRectangle () { int length; int width; length = readIntWithPrompt( "Rectangle length (a non-negative integer): "); width = readIntWithPrompt( "Rectangle width (a non-negative integer): "); this.rectangle = new Rectangle(length,width); }

20. 19May 2004Chapter 7 Building an interface for Rectangle ñRectangleTUI is a client of Rectangle. ñConstructor creates an instance of Rectangle using input values from user. ñBut, Rectangle has pre-conditions to keep:  User may enter negative values for length or width. public Rectangle (int length, int width) Create a new Rectangle with specified length and width. require: length >= 0 && width >= 0

21. 20May 2004Chapter 7 While statement condition true false statement END BEGIN while ( condition ) statement

22. 21May 2004Chapter 7 Re-implementing createRectangle private void createRectangle () { //initialize to insure at least one execution of loops: int length = -1; int width = -1; while (length < 0) length = readIntWithPrompt( "Rectangle length (a non-negative integer): "); while (width < 0) width = readIntWithPrompt( "Rectangle width (a non-negative integer): "); // assert: length >=0 && width >= 0 this.rectangle = new Rectangle(length,width); }

23. 22May 2004Chapter 7 Building an interface for Rectangle private void displayMenu () Display the menu to the user. private void executeChoice (int choice) Perform the indicated action, and display results to the user.

24. 23May 2004Chapter 7 Building an interface for Rectangle ñName operation choices with identifiers: private static final int LENGTH = 1; private static final int WIDTH = 2; private static final int AREA = 3; private static final int PERIMETER = 4; private static final int NEW = 5; private static final int EXIT = 0; private static final int NO_CHOICE = -1;

25. 24May 2004Chapter 7 Building an interface for Rectangle public void start () { createRectangle(); int choice = NO_CHOICE; while (choice!= EXIT) { displayMenu(); choice= readIntWithPrompt("Enter choice: "); executeChoice(choice); }

26. 25May 2004Chapter 7 Building an interface for Rectangle private void displayMenu () { System.out.println(); System.out.println("Enter number denoting action to perform:"); System.out.println("Display length............." + LENGTH); System.out.println("Display width.............." + WIDTH); System.out.println("Display area..............." + AREA); System.out.println("Display perimeter.........." + PERIMETER); System.out.println("Create new rectangle......." + NEW); System.out.println("Exit......................." + EXIT); }

27. 26May 2004Chapter 7 Building an interface for Rectangle private void executeChoice (int choice) { System.out.println(); if (choice == LENGTH) System.out.println("Length is " + rectangle.length()); else if (choice == WIDTH) System.out.println("Width is " + rectangle.width()); else if (choice == AREA) System.out.println("Area is " + rectangle.area()); else if (choice == PERIMETER) System.out.println("Perimeter is " + rectangle.perimeter()); else if (choice == NEW) createRectangle(); else if (choice == EXIT) System.out.println("Goodbye."); else System.out.println(choice + " is not valid."); }

28. 27May 2004Chapter 7 Using composition ñBuild an application that lets a user access a “locked oracle.” ñuser can get a fortune from oracle only by providing correct key. ñUse classes CombinationLock and Oracle. ñCreate two new classes, ñone modeling a locked oracle, and ñother defining user interface.

29. 28May 2004Chapter 7 Using composition public class Oracle A dispenser of fortunes. An Oracle gives a fortune only if it is awake; normal sequence of actions is: wake Oracle; get fortune; put the Oracle back to sleep. public Oracle () Create new Oracle. This Oracle is initially asleep. ensure: !this.isAwake() public boolean isAwake () This Oracle is awake. public String fortune () The prophecy currently seen by this Oracle. require: this.isAwake() public void awaken () Wake this Oracle. Oracle will divine a fortune when it wakes. public void sleep () Put this Oracle to sleep.

30. 29May 2004Chapter 7 Using composition public class LockedOracle A keyed dispenser of fortunes. A LockedOracle will give a fortune only if the correct key is provided. A LockedOracle must be told to conjure a fortune before the fortune can be retrieved. public static final String NO_FORTUNE String indicating no fortune has been conjured. public LockedOracle (int key) Create new LockedOracle with the specified key. require: 0 <= key && key <= 999 public String fortune () The prophecy currently seen by this LockedOracle. If a fortune has not been conjured, the String NO_FORTUNE is returned. public void conjureFortune (int keyToTry) Prophesy. This LockedOracle will make a prophecy only if the correct key is presented. require: 0 <= keyToTry && keyToTry <= 999

31. 30May 2004Chapter 7 Using composition  Composition: process of defining a new class by putting together existing classes. ñAn instance of the new class, the composite, references instances of the existing classes, its components.

32. 31May 2004Chapter 7 Implementing LockedOracle ñLockedOracle class defined to be a composite, with CombinationLock and Oracle components.

33. 32May 2004Chapter 7 Implementing LockedOracle ñInstance variables are initialized in constructor: private CombinationLock lock; private Oracle oracle; private String fortune; //current prophesy public static final String NO_FORTUNE = "Sorry, no fortune for you."; public LockedOracle (int key) { lock = new CombinationLock(key); lock.close(); oracle = new Oracle(); fortune = NO_FORTUNE; }

34. 33May 2004Chapter 7 Implementing LockedOracle  Command conjureFortune first attempts to open lock, and wakes oracle only if it succeeds: public String fortune () { return this.fortune; } public void conjureFortune (int keyToTry) { lock.open(keyToTry); if (lock.isOpen()) { oracle.awaken(); fortune = oracle.fortune(); oracle.sleep(); lock.close(); } else fortune = NO_FORTUNE; }

35. 34May 2004Chapter 7 Implementing the User interface class LockedOracleTUI A simple text-based interface for a LockedOracle. public LockedOracleTUI (LockedOracle oracle) Create a new interface for the specified LockedOracle. public void start () Run the interface.

36. 35May 2004Chapter 7 Implementing the User interface  Application creates an oracle and an interface, and executes interface’s start method: public class OracleExample { public static void main (String[] argv) { LockedOracle oracle = new LockedOracle(123); LockedOracleTUI ui = new LockedOracleTUI(oracle); ui.start() } }

37. 36May 2004Chapter 7 Implementing the User interface ñInstance variables and constructor. private LockedOracle oracle; private BasicFileReader in; public LockedOracleTUI (LockedOracle oracle) { this.oracle = oracle; this.in = new BasicFileReader(); }

38. 37May 2004Chapter 7 Implementing the User interface ñSpecify private helper methods: private boolean readYes (String prompt) Read a yes or no response from the user. Return true if user keys “yes.” private int readKey (String prompt) Read and return a legal key. ensure: 0 <= this.readKey() && this.readKey() <= 999

39. 38May 2004Chapter 7 Implementing the User interface public void start () { String fortune; boolean goOn = true; while (goOn) { goOn = readYes("Fortune? (Key yes or no): "); if (goOn) { int key = readKey("Enter key (0-999): "); oracle.conjureFortune(key); fortune = oracle.fortune(); System.out.println(fortune); System.out.println(); } System.out.println("Good-bye."); }

40. 39May 2004Chapter 7 Summary ñBuilt a simple text-based user interface. ñWe reviewed the relationship between client and server: ñ a client is dependent on its server, ña server is independent of its client.

41. 40May 2004Chapter 7 Summary ñIn designing a system, it is preferable to make stable components independent of those likely to require change. ñSince user interface is considerably less stable than model, we favor designs in which the user interface acts as client to the model. ñIn cases where model must collaborate with the user interface, need to minimize interface for this collaboration.

42. 41May 2004Chapter 7 Summary ñ Introduced i/o streams. ñA stream is a sequence of bytes, sometimes viewed as characters, to which an application can append data (an output stream) or from which an application can read data (an input stream). ñJava has an extensive library of classes to deal with streams. ñUse only basic functionality  from the predefined object System.out for output,  BasicFileReader class from nhUtilities.basicIO package for input.

43. 42May 2004Chapter 7 Summary ñ Presented two simple applications with their text- based user interfaces.  Introduced while statement or while-loop : a Java construct that specifies a sequence of actions to be repeated until a condition fails to hold.

44. 43May 2004Chapter 7 Summary ñ In design of LockedOracle composed existing classes to construct a new class. ñThe relation between a composite class and its component classes is called the has-a relation. ñLockedOracle class wraps Oracle, adapting its specification to that required by the system: the adapter pattern.