1. SOFTWARE AND PROGRAMMING 1 Lecture: MB33 7:30-9:00 (11&18.01.06 – from 6:00) Lab: B43, MB321, MB536 6:00-7:30 (from 25.01.06) EACH student must have obtained access to Birkbeck computing by 25.01.06 – otherwise no use in the lab Instructor: Prof. Boris Mirkin SCSIS, room 111, tel. 020 7631 6746 E-mail: mirkin@dcs.bbk.ac.uk Course Assistants: 1) Two of the labs: SCSIS PhD students 2) WebCT/Tests/Assignments: Marie-Helene Ng SCSIS, room NG26, tel. 0207 631 6550 E-mail: marie-helene@dcs.bbk.ac.uk

2. SOFTWARE AND PROGRAMMING 1 Lecture: MB33 7:30-9:00 (except 11&18.01.06) Lab: SHB43, MB321, MB536 6:00-7:30 (from 25.01.06) Each student must have obtained access to Birkbeck computing to be able to learn programming in real at lab sessions. To be able to submit your assignment you must send your CCS username to Marie-Helene Ng by 31 January. E-mail: marie-helene@dcs.bbk.ac.ukmarie-helene@dcs.bbk.ac.uk

3. 3 Webpages The course web page is at www.webct.bbk.ac.uk www.webct.bbk.ac.uk Please check it regularly. It will be used for announcements and assignments. Another, open, page at my web- site will function with lecture notes and other relevant materials: www.dcs.bbk.ac.ukwww.dcs.bbk.ac.uk/~mirkin/sp105

4. 4 Texts 1.David J. Barnes & Michael Kölling Objects First with Java: A Practical Introduction using BlueJ, Second edition, Pearson Education, 2005, ISBN 0-13-124933-9 The publisher supplies a helpline (team’s telephone included) in installing the related software 2. J. Farrell Java Programming, Second edition, Course Technology, Thompson, 2003, ISBN 0-619-21500-3 3. I. Pohl, C. McDowell Java by dissection, Addison-Wesley, 2000, ISBN 0201751585 4. Free: ON-LINE text by D. Eck (on my web site) and other useful URLs

5. 5 Teaching Goal: Coding in Real FRAMEWORK: 1. the work of a compiler and an interpreter; 2. classes and instances; 3. variables and static variables; 4. data and number types in Java; 5. arithmetic and Boolean expressions; 6. for/while and if…elseif…else structures; 7. processing strings; 8. elements of input/output in Java; 9. methods and constructors; 10. arrays and their usage.

6. 6 Teaching Goal PRACTICE: To have developed skills in practical programming of small but real-world problems e.g. keeping transaction records, assigning seats to customers, managing a bus schedule, etc.

7. 7 Control Final exam: 75% of mark Course-work: 25% of mark –2 open-book in-class tests, 8.02 & 8.03, –2 assignments for home work via WebCT Composition of CW 25% mark: T15% T27% A15% A2 8%

8. 8 Control: Example Let marks of a student be as follows: –Exam:50 –T112 –T265 –A1100 –A20 (hasn’t submit) The total mark will be 48 because 50*0.75 + 12*0.05 + 65*0.07 + 100*0.05 + 0*0.08= =37.5 + 0.6 + 4.55 + 5 + 0 = 47.65

9. 9 Teaching Philosophy (extracts) Huge respect for part-time students The bulk of students to get taught No student’s question is stupid Simple things learnt well: rather than complex things not learnt well Instructor’s small errors: OK as a teaching device if noticed and corrected Instructor’s slowness: a device to raise students’ awareness (no time waste)

10. 10 Why Java Object-oriented (a program is a set of classes sending messages to each other with methods within to process inputs), which is useful for code transfer and maintenance Network-oriented (server-to-clients) Works within Internet browsers [devices viewing HTML (hyper-text markup-language) documents via HTTP (hyper-text transfer protocol) links]

11. 11 Fundamental concepts Java as is and Java with BlueJ Object Class Method Parameter Variable Data type

12. 12 High-language code to machine code translated A compiler takes a high-level-language program and translates it as a whole into an executable machine-language program. Once the translation is done, the machine-language program can be run any number of times, but of course it can only be run on one type of computer. Thus, each type of computer requires a specific translator. An interpreter is a program that runs in a loop in which it repeatedly reads one instruction from the program, decides what is necessary to carry out of that instruction, and then performs the appropriate machine-language commands to do so. This is slow but universal.

13. 13 source file 011010 110101 010001 class file 011010 110101 1001 10 1 0111 0110110 1 1 editor compiler (javac) virtual machine (java interpreter) Java edit-compile-interpret-execute cycle

14. 14 Two JAVA environments Java Developer Kit JDK (currently, J2SE) (Conventional) Blue J (A public project to make JAVA coding easier) –Both available in Birkbeck

15. 15 Conventional JDK: Editing A source code can be edited in any text editor: Notepad, emacs, PFE,... MS Word caveat: by default, Word does not save in ASCII text format Make sure to save the code before compiling! The file name: the same as that of the class, with extension: say, class NicTe{…} must be saved as file NicTe.java, case sensitive

16. 16 Command line invocation compilation and execution of Java in JDK are done from a command line On Microsoft systems: DOS shell On Unix: Unix shell Must make sure that the commands for compiler and runtime (JVM) are in the command path.

17. 17 Compiling with JDK Name of the JDK compiler: javac To invoke: javac compiles and all classes it depends on into an executable on JVM file.class Example: javac NicTe.java produces file NicTe.class

18. 18 Execution “java” starts the Java virtual machine: java NicTe The named class is loaded and execution is started. Other classes are loaded as needed. Only possible if class has been compiled into a file, say, NicTe.class

19. 19 JDK Problem: Execute what? How does the system know which method to execute?

20. 20 The main method in JDK The JDK java system always executes a method called main with a certain signature: Signature _______________________ public static void main(String[] args) {... } To work with JDK, such a method must be present in your program!

21. 21 A simplest program /* HelloWorld.java Purpose: printing a message to the screen */ class HelloWorld { // Each program is organised as a class public static void main(String[] args) { System.out.println("Hello World!"); } } // end of class HelloWorld /* Always Three Types of Elements ONLY: comments class (with modifiers) methods (with modifiers and parameters)*/

22. 22 BlueJ coding BlueJ programs are organised in the so-called projects A BlueJ project is stored in a directory on disk Some files store the source code, some store the compiled code, some store additional information.

23. 23 The BlueJ directory structure UserInterface CalcEngine Calculator project: calculator c:\bluej\calculator\ bluej.pkg bluej.pkh Calculator.java Calculator.class Calculator.ctxt UserInterface.java UserInterface.class UserInterface.ctxt CalcEngine.java CalcEngine.class CalcEngine.ctxt

24. 24 The BlueJ file structure bluej.pkg - the package file. Contains information about classes in the package. One per package. bluej.pkh - backup of the package file. *.java - standard Java source file (text). One per class. *.class - standard Java code file. One per class *.ctxt - BlueJ context file. Contains extra information for a class. One per class.

25. 25 Available on BBK’s network –Java JDK (which allows you to compile and execute your program) –BlueJ (Preferred editor) Installing BlueJ (for home use) –First download the Java JDK from http://java.sun.com/j2se/1.5.0/download.jsp –Download BlueJ from http://www.bluej.org/download/download.html http://www.bluej.org/download/download.html –Run “ bluejsetup-202.exe” and follow the given instructions Software is free

26. 26 Objects and classes Classes: program templates –represent all objects of a kind (example: “student”) Objects = instances –A template copy to represent a specific element of the class (“an individual student”) –Instances are created with the so-called constructors, explicit in JDK or somewhat easier in BlueJ

27. 27 Variables, methods and parameters classes contain data stored in the so- called variables and operations which can be invoked (they are called methods in Java) methods may have inputs (they are called parameters in Java) to get additional data needed to get them executed

28. 28 Remarks Many instances can be created from a single class An object has attributes/variables: values stored in fields (memory locations). The class defines what fields any its object has (a template), but each object may store its own set of values (the state of the object) A variable is initialised with assigning it a value, an object – with a constructor

29. 29 More on Method Method in Java is a named set of instructions that transforms some input into an output. This is, actually, a machine implementation of the concept of algorithm which itself is a computational analogue to the mathematical concept of function. Static method: is shared by all instances.

30. 30 Example of a method (1) Square function y = x 2 x y 1 2 4 5 25 11 121 The table can be used for invoking a specific value, like, 7 2 = 49 or 10 2 = 100.

31. 31 Example of a method (2) A Java method to calculate the square function: public int sq(int x){ return x  x;} To make it work, variables are needed: int sevs=sq(7); //puts 49 into sevs int tens=sq(10); // puts 100 into tens

32. 32 Structure of a method modifiers return-type name ( parameter-list ) { statements; return variable/expression; //if return type is not void } Modifiers: –static - method/variable that belongs to class as whole and is shared by all –public - method/variable that is accessible from anywhere –private - method/variable that is accessible from only within the class Output’s typeInputs

33. 33 HelloWorld with a method // Hello-world program to demonstrate BlueJ class Hello{ // Method that does the work of printing public void go() { System.out.println("Hello, world"); } // main method for working outside BlueJ public static void main(String[] args) {Hello hi = new Hello(); //instance hi.go(); //method in instance hi }

34. 34 Fields Fields store values for an object. They are also known as instance variables. Use the Inspect option to view an object’s fields. Fields define the state of an object. public class TicketMachine { private int price; private int balance; private int total; Constructor and methods omitted. } private int price; visibility modifiertypevariable name

35. 35 Assigning values Values are stored into fields (and other variables) via assignment statements: –variable = expression; –price = ticketCost; The value on the right is assigned to a variable on the left. A variable stores a single value, so any previous value is lost.

36. 36 Variable It provides for multiple uses of the same program A variable is a name for a location in memory that can hold data. Variables are declared and/or initialised A variable declaration includes the following: –A data type that identifies the type of data that is stored in the variable –An identifier that is the variable’s name –An optional assigned initial value

37. 37 int p; p p = 4; 4 In memory:

38. 38

39. 39 Scope of a variable: The range of statements that can access the variable. It stretches from the declaration point to the end of the block containing the declaration Q: WHAT is BLOCK ? (part within curly braces{…} ) Q: WHAT is DECLARATION? (type name ; 3-part command)

40. 40 BlueJ HelloWorld N times public class HelloN { int number; \\ variable declared public void go() { System.out.println("Hello, world"); } public HelloN(int howmany) {number=howmany; } \\constr-r to initialise an object public void prrt() \\printing number times { for(int i=1;i<=number;i++) \\loop go(); System.out.println("ok"); } }

41. 41 Arithmetic Operators * 5  3=15 /36/9=4, 39/9=4, 39/50=0 (integers) /36.0/9=4.0, 39.0/9=4.33333333, 39.0/50=0.78 (reals) %36%9=0, 39%9=3, 39%50=39 +5 + 3 = 8 -5 – 3 = 2 Other operators such as Abs or exp are in class Math of Java (to be later)

42. 42 Arithmetic Expressions 2 * 6 / 4 + 5 – 2 * 3 = 3 + 5 – 6 = 2 2 * 6.0 / (4 + 5) – 2 * 3 = 12.0/9 – 6 = – 4.67 (note: reals, not integers) 2 * 6 / 4 + (5 – 2) * 3 = 12

43. 43 Basic class structure public class TicketMachine { Inner part of the class omitted. } public class ClassName { Variables Constructors Methods } The outer wrapper of TicketMachine The contents of a class

44. 44 Concepts mentioned Compiler & interpreter JDK/JDS and BlueJ environments Method Variable; declaration and intialisation Primitive variable types Arithmetic operators and expressions Class and instance HelloWorld class in different versions