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SOFTWARE AND PROGRAMMING 1 EACH student must have obtained access to Birkbeck computing by 26.01.11 – otherwise no use in the lab Instructor: Prof. Boris.

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Presentation on theme: "SOFTWARE AND PROGRAMMING 1 EACH student must have obtained access to Birkbeck computing by 26.01.11 – otherwise no use in the lab Instructor: Prof. Boris."— Presentation transcript:

1 SOFTWARE AND PROGRAMMING 1 EACH student must have obtained access to Birkbeck computing by – otherwise no use in the lab Instructor: Prof. Boris Mirkin DCSIS, room 744 MAL, tel Course Assistant: Lab/WebCT/Tests/Assignments: Mr Martin OShea (FROM 26 January: Lectures , Labs )

2 2 Webpage The course web page is currently at my open web-site, with lecture notes and other relevant materials:

3 3 Texts: Any, including 1.Quentin Charatan & Aaron Kans [CK] JAVA in Two Semesters, 2nd Edition, McGraw-Hill, 2006, ISBN David J. Barnes & Michael Kölling [BK] Objects First with Java: A Practical Introduction using BlueJ, 2nd edition, Pearson Education, 2005, ISBN The publisher supplies a helpline in installing related software 3. I. Pohl, C. McDowell [PM] Java by dissection, Addison-Wesley, 2000, ISBN J. Farrell [F] Java Programming, 2-4 editions, Course Technology, Thompson, , ISBN etc. 5. Free: ON-LINE text by D. Eck (on my web site); other URLs

4 4 Teaching Goal: Coding in Real FRAMEWORK: 1. the interpreter/compiler Java working; 2. classes, objects and instances ; 3. variables and static variables ; 4. Java data types: primitive and user-defined ; 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, including arrays of a user-defined type

5 5 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.

6 6 Control Final exam: 75% of mark Course-work: 25% of mark –2 open-book in-class tests, 9.02 & 9.03, –2 assignments for home work via WebCT, & Composition of CW 25% mark: T15% T27% A15% A2 8%

7 7 Control: Example Let marks of a student be as follows: –Exam:50 –T112 –T265 –A1100 –A20 (hasnt submitted) The total mark will be 48 because it rounds up the result: 50* * * * *0.08= = = 47.65

8 8 Teaching Philosophy (extracts) Huge respect for part-time students The bulk of students to get trained No students question is stupid since Software is invented Better to have simple things learnt well rather than complex things learnt not well Instructors small errors - a good teaching device for activation of the students brain Learning a language in a college differs from consuming a lunch in a diner in many ways Fast feedback on students issues if raised

9 9 OOP concepts you already know of How a Java program works: interpret/compile Variable Expression Data type Loop If/elseif/else structure Class Method Parameter These will be expanded to more realistic environments

10 10 Two JAVA environments Will be using both: Java Developer Kit JDK (currently, J2SE) (Conventional) Blue J (A public project to make JAVA coding easier)

11 11 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, case sensitive

12 12 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.

13 13 Getting JDK on a systems path Click Properties on right-buttoned My computer Click Advanced Click Environmental variables Enter new path (to the directory in which javac.exe and java.exe reside)

14 14 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 produces file NicTe.class

15 15 Execution in JDK 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

16 16 JDK Problem: Execute what? How does the system know which of the methods in a class to execute?

17 17 main method in JDK BlueJ executes what the user says; The JDK java system always executes a method called main, it should have a certain signature: Signature _______________________ public static void main(String[ ] args) {... } To work with JDK, such a method must be present in your program!

18 18 A primer program (=class) /* 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 & parameters/arguments)*/

19 19 BlueJ coding BlueJ programs are organised in the so-called projects A BlueJ project is stored in a project- specific directory on disk Some files store the source code, some store the compiled code, some store additional BlueJ related information.

20 20 The BlueJ directory structure UserInterface CalcEngine Calculator project: calculator c:\bluej\calculator\ bluej.pkg bluej.pkh Calculator.class Calculator.ctxt UserInterface.class UserInterface.ctxt CalcEngine.class CalcEngine.ctxt

21 21 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.

22 22 Available on BBKs 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 –Then download BlueJ from –Run bluejsetup-202.exe and follow the given instructions Software is free

23 23 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, explicitly in JDK or somewhat easier in BlueJ

24 24 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 have them executed

25 25 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

26 26 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.

27 27 Example of a method (1) Square function y = x 2 x y The table can be used for invoking a specific value, like, 7 2 = 49 or 10 2 = 100.

28 28 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

29 29 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 instances –public - method/variable that is accessible from anywhere –private - method/variable that is accessible from only within the class Outputs typeInputs

30 30 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 }

31 31 HelloWorld : WHY Why dots in System.out.println("Hello, world"); hi.go(); ? 1)To take method from a specific class instance 2)To take a class from a set of classes: Java is organised as a hierarchically structured set of classes in individual files

32 32 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.

33 33 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 variables name –An optional assigned initial value

34 34 int p; p p = 4; 4 In memory:

35 35

36 36 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)

37 37 HelloWorld N times BlueJ public class HelloN { int number; \\ variable declared public void go() { System.out.println("Hello, world"); } public HelloN(int howmany) {number=howmany; } \\constr to initialise object public void prrt() \\printing number times { for(int i=1;i<=number;i++) \\loop go(); System.out.println("ok"); }}

38 38 Loop for for(int var=1;var<=st;var++){ do operation depending on var } Two types of parentheses: () and {} The expression in () consists of three different items: initialising a variable, variable update, and stop-condition Given a value of var, {} is executed, after which var is updated, then stop-condition checked and, if yes, {} is executed again; if no, the program proceeds further on

39 39 No { } in for-loop in HelloN Why? Let us add { }: where? Is there any difference between before and after ok?

40 40 Arithmetic Expressions 2 * 6 / – 2 * 3 = – 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 Java uses a natural precedence structure of arithmetic operations. If you are not sure, use parentheses!!!

41 41 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

42 42 Concepts considered: overview Compiler & interpreter JDK/JDS and BlueJ environments Method Variable; declaration and intialisation Primitive variable types Class type Arithmetic operators and expressions Class and instance HelloWorld class in three versions

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