Download - SOFTWARE AND PROGRAMMING 1
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 MirkinDCSIS, room 744 MAL, tel. 020 7631 6746E-mail: [email protected]
Course Assistant:
Lab/WebCT/Tests/Assignments: Mr Martin O’SheaE-mail: [email protected]
(FROM 26 January: Lectures 6.00-7.30, Labs 7.30-9.00)
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Webpage
The course web page is currently at my open web-site, with lecture notes and other relevant materials:
http://www.dcs.bbk.ac.uk/~mirkin/sp109
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Texts: Any, including1. Quentin Charatan & Aaron Kans [CK]
JAVA in Two Semesters, 2nd Edition, McGraw-Hill, 2006, ISBN-10 0077108892
2. David J. Barnes & Michael Kölling [BK]Objects First with Java: A Practical
Introduction using BlueJ, 2nd edition, Pearson Education, 2005, ISBN 0-13-124933-9The publisher supplies a helpline in installing related software
3. I. Pohl, C. McDowell [PM]Java by dissection, Addison-Wesley, 2000,
ISBN 02017515854. J. Farrell [F]
Java Programming, 2-4 editions, Course Technology, Thompson, 2003-7, ISBN 0-619-21500-3 etc.
5. Free: ON-LINE text by D. Eck (on my web site); other URLs
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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
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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.
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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,
9.02-9.03 & 23.02-23.03
Composition of CW 25% mark: T1 5% T2 7% A1 5% A2 8%
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Control: Example• Let marks of a student be as follows:
– Exam: 50– T1 12– T2 65– A1 100– A2 0 (hasn’t submitted)
• The total mark will be 48 because it rounds up the result:
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
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Teaching Philosophy (extracts)
• Huge respect for part-time students• The bulk of students to get trained• No student’s question is stupid since
Software is invented• Better to have simple things learnt well
rather than complex things learnt not well• Instructor’s small errors - a good teaching
device for activation of the student’s 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
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OOP concepts you already know of• How a Java program works: interpret/compile
• Variable
• Expression
• Data type
• Loop
• If/elseif/else structure
• Class
• Method
• ParameterThese will be expanded to more realistic environments
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Two JAVA environments• Will be using both:
• Java Developer Kit JDK (currently, J2SE) (Conventional)
• Blue J (A public project to make JAVA coding easier)
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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
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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.
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Getting JDK on a system’s 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)
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Compiling with JDK
• Name of the JDK compiler: javac• To invoke:javac <source name>
• compiles <source name> and all classes it depends on into an executable on JVM file <source name>.class
• Example:
javac NicTe.javaproduces file NicTe.class
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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
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JDK Problem: Execute what?
How does the system know which of the methods in a class to execute?
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“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!
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A primer program (=class)/* 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 & parameters/arguments) */
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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.
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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
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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.
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• 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/1.5.2/download.jsp– Then download BlueJ from
http://www.bluej.org/download/download.html
– Run “bluejsetup-202.exe” and follow the given instructions
Software is free
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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
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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
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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
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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.
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Example of a method (1)Square function y = x2
x y 1 1 2 4 5 2511 121
The table can be used for invoking a specific value, like, 72 = 49 or 102 = 100.
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Example of a method (2) A Java method to calculate the square function:
public int sq(int x){return xx;} To make it work, variables are needed:
int sevs=sq(7); //puts 49 into sevs
int tens=sq(10);// puts 100 into tens
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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
Output’s type Inputs
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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
}}
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HelloWorld : WHY
Why dots in System.out.println("Hello, world"); hi.go();
?1) To take method from a specific class
instance2) To take a class from a set of classes: Java is
organised as a hierarchically structured set of classes in individual files
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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.
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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
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int p;
p
p = 4;
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In memory:
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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)
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HelloWorld N times BlueJpublic 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"); } }
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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
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No { } in for-loop in HelloN
Why?Let us add { }: where?
Is there any difference
between before and after “ok”?
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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
Java uses a natural precedence structure of arithmetic operations. If you are not sure, use parentheses!!!
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Basic class structure
public class TicketMachine{ Inner part of the class omitted.}
public class ClassName{ Variables Constructors Methods}
The outer wrapperof TicketMachine
The contents of aclass
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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