EECS1710. Announcements. epost updated, please check online Next Labtest: Thu Oct 23/Fri Oct 24. Next Term Test: Tue Oct 28.

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1 EECS1710 Click to edit Master Week text 06, styles Lecture 11 Second level Third level Fourth level Fifth level Fall 2014! Tuesday, Oct 14, Announcements epost updated, please check online Next Labtest: Thu Oct 23/Fri Oct 24 covers Ch 2 & 3 Next Term Test: Tue Oct 28 covers Ch 3 & 4 2 1

2 Checklist from prev lecture (Oct 9, 2014) What you should be doing to prepare for what comes next " read section 3.2 A Development Walk-Through " review Ch 3 KC s 7-14 " do Ch 3 RQ s " do Ch 3 Ex s Have a Happy Thanksgiving Holiday 3 Plan for today The Development Process The Mortgage App students review on their own Output Formatting Relational Operators and Input Validation Input Validation Assertions - students review on their own 4 2

3 3.2.1 The Development Process A methodology is a system of methods used in a particular activity A software development methodology is a system of methods used in in order to develop software that is correct, usable, robust, (and other desirable characteristics) The development process described in the textbox is called the iterative methodology. It is the core technology-centered design methodology Please be aware that the this technology-centered approach stands in contrast with Human-Centered Design (HCD), which is an approach that is better suited when designing for usability The Development Process REQUIREMENTS can you describe each of these phases? what is the pur:ose of each one? DESIGN IMPLEMENTATION TESTING DEPLOYMENT 6 3

4 3.2.1 The Development Process Comprehension Questions What is the difference between the requirements analysis phase and the design phases? At what stage does coding take place? At what stage would the designer create UML class diagrams? In the implementation stage, how does the implementer know what functionality should be implemented? In the testing phase, a set of test cases are uses to assess correctness. What is the basis for the creation of these test cases? The Mortgage App Students should review this material on their own and be prepared to be able to answer related questions on the test 8 4

5 3.2.3 Output Formatting: Available Services By now, we have employed println, print, and printf : Which class(s) offers these services? Discuss overloading: is printf an overloaded method? is print an overloaded method? is println an overloaded method? How are print and println similar? How are they different? Is printf more similar to print or to println? Output Formatting: Comprehension What is the return of print and println? How are print and println similar? How are print and println different? 10 5

6 3.2.3 Output Formatting: printf Signature of printf is as follows: printf(string format, Object... args) This means at least one arg, format and then zero or more additional args Now let's discuss this format string further Output Formatting: printf The format string is a String which may contain fixed text and zero or more embedded format specifiers Idea #1: The format specifiers are optional and the args are optional Consider what happens when you leave out the format specifiers and only make use of fixed text stdout.printf("hello"); stdout.printf("56"); stdout.printf("56\n"); only the for;at st<ing & no args stdout.printf("\t56\n"); printf(string format, Object... args) 12 6

7 3.2.3 Output Formatting: printf The most basic conversion for the format specifier is %s. Idea #2: there must be an arg for each format specifier Consider the following stdout.printf( hello%s,56f); stdout.printf( 56%s,4L); stdout.printf( 56%s%s%s\n,33,88.7, hi ); stdout.printf( %s\t56\n, ); stdout.printf( %s, "hello"); Output Formatting: printf The \n string is equivalent to the format specifier %n. Consider the following: stdout.printf( hello\n ); stdout.printf( hello%n ); 14 7

8 3.2.3 Output Formatting: printf The d conversion character takes int/long args The f conversion character takes float/double args Idea #4: Use these conversion characters Consider the following: stdout.printf( ans: %d%n,56); stdout.printf( ans: %d%n,56l); stdout.printf( ans: %f%n,56.67); stdout.printf( ans: %f%n,56.67f); 15 In case of mismatch, what happens? Output Formatting: printf Idea #5: The width component specifies the number of characters for the output. The width component can be used with %s, %d, %f. The output is right justified. Consider the following: stdout.printf("ans: %10s%n", "hi"); stdout.printf("ans: %10d%n", 56); stdout.printf("ans: %10f%n", ); 16 8

9 3.2.3 Output Formatting: printf Idea #6: The precision component specifies the number of decimal digits for %f with float/double. It cannot be used with the%s for or the %d specifiers Consider the following: stdout.printf("ans: %10.2s%n", "hi"); stdout.printf("ans: %10.2d%n", 56); stdout.printf("ans: %10.2f%n", ); Output Formatting: printf Idea #7: The flag component can be, and/or 0. It can be used only with numerical types Consider the following: stdout.printf("ans: %010d%n", 5666); stdout.printf("ans: %,10d%n", 5666); stdout.printf("ans: %0,10d%n", 5666); stdout.printf("ans: %010.2f%n", ); stdout.printf("ans: %,10.2f%n", ); stdout.printf("ans: %0,10.2f%n", ); 18 9

10 3.2.3 Output Formatting: printf The general form of each specifier is: %[flags][width][.precision]conversion conversion letter can be: d : int/long f : float/double s : string n : new line width: how many characters to be allocated flags can be:, and/or 0 precision: # of decimal digits (for f conversion letter only) Output Formatting: printf In what crucial way is the signature of printf different from the signatures of print and println? Is printf more similar to print or to println? Is printf an overloaded method? How can printf be used to mimic print or println? Replicate the behaviour of print(67.8) Replicate the behaviour of println( hello ) 20 10

11 3.2.4 Relational Operators Numeric operands: < <= > >= Numeric/boolean operands (any type): ==!= A special infix operator: instanceof All relational operators violate closure (*except boolean equality operator) No matter what the operand type is, the result type is always boolean. 21 Operator Precedence precedence level of the assig>ment operator = is -15 (p.33, p.110) precedence levels of arithmetic operators can be found on p. 27 Precedence Operator Operands Syntax true if < numeric x < y x is less than y <= numeric x <= y x is less than or equal to y -7 # > numeric x > y x is greater than y >= numeric x >= y x is greater than or equal to y instanceof x instanceof C is true if object reference x points at an instance of class C or a subclass of C. -8 # == any type x == y x is equal to y!= any type x!= y x is not equal to y 22 11

12 3.2.4 The equality operator Be certain that you understand the difference between the following: the assignment operator = the equality operator == The equality operator Be certain that you understand the behaviour of the equality operator with primitive operands boolean isequal1 = 7812 == ; boolean isequal2 = 'a'=='b'; boolean isequal2 = 'a'+1=='b'; 24 12

13 3.2.4 The equality operator Be certain that you understand the behaviour of the equality operator with non-primitive operands Rectangle r1 = new Rectangle(10, 10); Rectangle r2 = new Rectangle(10, 10); Rectangle r3 = new Rectangle(20, 20); boolean isequal1 = r1==r2; boolean isequal2 = r1==r3; Assertions Students should review this material on their own and be prepared to be able to answer related questions on the test A key point: assertions are intended to be used only during development; once testing is completed and the app is going into production, all of the assert statements are disabled 26 13

14 3.2.5 Input Validation Students will have noticed that we have already been performing input validation during the lab exercises; all of this material should already be familiar!! 27 Topic: Working with files We will cover some basic material about files during lecture and then do some exercises on the lab exercises (see 5.3.2) Our motivation is that we will start to work with manipulating images, which requires working with the file system working with images also requires working with the operating system s window manager and the platform s graphics hardware, understanding colour models and colour representation formats and being able to iterate and construct conditions we will cover each of these topics over the next few lectures 28 14

15 Topic: Working with files Any file on the hard drive has a pathname and the details of this path name depend on the operating system Here are some examples 29 Windows Local File System (LFS) C:\USER\DOCS\LETTER.TXT Windows Uniform Naming Convention (UNC) \\Server\Volume\File Unix-like OS /home/user/docs/letter.txt" Topic: Working with files The format of a pathname is consistent across the different OS's, but the details differ C:\USER\DOCS\LETTER.TXT \\Server\Volume\File /home/user/docs/letter.txt" " Here are the consistent features the system prefix (e.g., C:\, \\, /) # the separator (e.g., \,/) #File.separator 30 15

16 Topic: Working with files The class java.io.file provides services for working with the file system on your hard drive For this class, a file can be either a directory a normal file (i.e., not a directory) 31 Topic: Working with files The class java.io.file is NOT a utility class The class has several constructors. We will be using the constructor that takes a String parameter: File(String) The passed String is a pathname It can be a pathname to a file that doesn't exist yet (and that you will create) It can be a pathname to a file that already exists (and from which you want to read) 32 The File class encapsulates services for both potentially-existing files and already-existing files. 16

17 Topic: Working with files How can we specify a pathname so that it is compatible for any operating system? The class File has a static field that provides the separator that is in use on the system: File.separator The VM will ensure the field is assigned a String value that reflects the current OS on Windows, it will be "\" on Unix-like OS's (including Mac OS X), it will be "/" 33 UML Class Diagram for File just because an object is instantiated for a pathname doesn t necessarily mean that there is an actual file corresponding to that pathname! java::io::file! +separator: String" " File(String)" " +exists(): boolean" +lastmodified(): long" +length(): long" +getpath(): String" " 34 17

18 Services provided by the File class"! provides constructor for object creation, given a pathname#! demo: File_Example01#! provides delegation of file-related tasks:#! does this file exist?#! is this file a directory or a normal file?#! what is the size of this file?#! can I write to this file? #! which files are in this directory, if any?#! assumes this file is a directory#! make a directory, as specified by this file#! assumes pathname is not already in use and operation is allowed ## 35 35# Services provided by the File class"! Additional services#! can I write to this file? #! which files are in this directory, if any?#! assumes this file is a directory#! make a directory, as specified by this file#! assumes pathname is not already in use and operation is allowed ## 36 36# 18

19 The encapsulation of a File " ##! provides services to ask whether the file is writable!! this tells you whether the permissions and other conditions are favourable#! the File class does not provide the means to write to the file object $#! for this, you need the services of FileWriter"! a FileWriter object encapsulates all of the working of writing content to a File object#! defer this aspect for the time being# 37 37# Another way to interface with the file system " ##! Use the services of the Swing package, which has a class called JFileChooser! let the user specify one for you#! FileChooser_Example # 19

20 the JFileChooser class # getselectedfile() will always return something, # even before the dialog is even opened# java::swing::jfilechooser! +APPROVE_OPTION: int" +CANCEL_OPTION: int" JFileChooser()" " +showopendialog(null): int" +getselectedfile(): File" " JFileChooser encapsulates information about and operations on a file choice dialogue.# 39 39# Checklist (for next time, Lecture 13) What you should be doing to prepare for what comes next " read section 3.3 " review Ch 3 all key concepts, all review questions, remainder of exercises " do Ch 3 Exercises (up to 3.17 definitely, ) " Exercise 3.23 is a practise test (link to textbook website can be found on course website) 40 20