SOFTWARE AND PROGRAMMING 1

Lecture: Gor B4 7:40-9:00 (from 24.01.07)Lab: SH131, BBK536 6:00-7:30 (from 24.01.07)[each student must have obtained access to Birkbeck

computing]

Lab SH131: students whose family names (surnames) begin A-L

Instructor:Ms Marie-Helene NgSCSIS, room NG26, tel. 020 7631 6725 E-mail: marie-helene@dcs.bbk.ac.uk

Lab BBK536 : students whose family names (surnames) begin M-Y

Instructor: Prof. Boris MirkinSCSIS, room 111, tel. 020 7631 6746E-mail: mirkin@dcs.bbk.ac.uk

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Webpages

Course web page at webCT: http://vle.bbk.ac.uk

Please check it regularly. It will be used for announcements and assignments.Another page, at an open-to-all web-site, functions with relevant materials too:www.dcs.bbk.ac.uk/~mirkin/sp105

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Formerly Recommended Texts

1. David J. Barnes & Michael KöllingObjects First with Java: A Practical

Introduction using BlueJ, Second edition, Pearson Education, 2005, ISBN 0-13-124933-9The publisher supplies a helpline (team’s telephone included) in installing the related software

2. J. FarrellJava 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

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Currently Recommended Text

Q. Charatan, A. KansJava in Two Semesters, Second edition, The

McGrow-Hill Education, 2006, ISBN 978-0-07-710889-2

In fact, either will do.One more:Edward Currie (2006), Fundamentals of Programming Using

Java, Thomson Learning, ISBN-10: 1-84480-451-8.

This book contains well explained examples but covers not all thematerial: an excellent text for slow learners.

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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/1.5.0/download.jsp– 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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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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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

• “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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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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Concepts from lecture 1• Compiler (javac.exe) and

Interpreter (java.exe), should be on system’s path

• JDK and BlueJ for running Java• Class (template) and Object (its

instantiation); every Java program must be a class

• Variable and its type; primitive types• Method (input-output operation)

and its Parameters (inputs - with their types at method’s declaration)

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Concepts to be learnt

• Arithmetic expression and precedence

• Casting• Boolean expression• Statement• Loops for, while• Choice structure if/elseif/else

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Five arithmetic operations in Java

• * multiplication 53=15

• / division 36/9=4, 39/9=4, 39/50=0 (integers)

36.0/9=4.0, 39.0/9=4.3333333, 39.0/50=0.78 (reals)

• % remainder 36%9=0, 39%9=3, 39%50=39

• + summation 5 + 3 = 8

• - subtraction 5 – 3 = 2

• Other operators such as Abs or exp or log are in class Math of Java (to be explained later)

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Arithmetic expressions• Precedence: */% first, then +- 

If not sure, use (…): first performed inside

• 2 * 6 / 4 + 5 – 2 * 3 = 3 + 5 – 6 = 2 (integers)

• 2 * 6.0 / (4 + 5) – 2 * 3 = 12.0/9 – 6 = – 4.67 (reals are here)

• 2 * 6 / 4 + (5 – 2) * 3 = 12

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Unifying TypeUnifying Type:   The type of result when calculations

use different types

 Order for Implicitly Establishing Unifying Type:•              double•              float•              long•              int•              short•              byte

 

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Type casting

      The unifying type can be overridden by explicitly stating a type cast:

• Place the desired type result in parentheses followed by the variable or constant to be cast

•      (int) 6.0+7=13

• Example:

• int bankbalance=931786;

float weeklybudget = (float) bankbalance /4;

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Boolean expressions: true or false• |, || or• &, && and• ! not• == equal to• < less than• > greater than• <= < or ==• >= > or ==Always after arithmetic; If not sure,

useparentheses (…): first performed

inside

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Condition

int x=2;x+4*2>5 true

at what x is this false?

int x=3;int y=1;x-4 == 1.5*(y+2)

can this be true?

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Precedence table

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Loop forfor(int var=1;var<=st;var++) % no ‘;’ here!!!{do operation depending on var}var++ is var=var+1 , not var=var+2;

• Two types of parentheses: (loop specified) and {body to do}• The expression in () consists of three items in this order:

– initialising the counting variable once, – variable update, and – stop-condition

• First, – var is intialised, – stop-condition is tested;

• if true, block {} is executed,• if no, the program proceeds further on, after the block { }

– control returns to ( ) • After control returns to ( ),

– var is updated; – stop-condition is checked;

• if true, block {} is executed, then control returns to ( ), • if no, the program proceeds further on, after the block { }

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Loop while: less rigid for(init; test; update){ statements }

All three in the parentheses refer to a counter that is initialised, updated and tested over reaching the pre-specified threshold

Structure of while loop, less rigid – init, test and update are not necessarily based on counter:

init; while(test){ statements;

update } Similar elements: ( ), { }, initialisation, test

condition (not necessarily involving the counter!), and update

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Example:

for (int K = 10; K > 1 ; K--) {

//k-- is k=k-1;

if (K < 7) { break; } // Stops execution of the loop

else

System.out.print(“ ” + K);

}

1. What this loop does?

2. Can it be rewritten in the while format?

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Example: answer 1 for (int K = 10; K > 1 ; K--) {

if (K < 7)

{ break; }

else

{ System.out.print(“ ” + K);}

}

What this loop does?

Prints 10 9 8 7

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Example: answer 2 int K = 10;

while(K >1) {

if (K< 7)

break;

else

System.out.print(“ ” + K);

K--;

}

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Simplest program/* HelloWorld.java Purpose: printing a message to the screen */ class HW {

// Each program is organised as a class         public static void main(String[] args)

{          System.out.println("Hello, World!");         } } // end of class HW /* Always Three Types of Elements ONLY: • comments• class (with modifiers)• methods (with modifiers and parameters) */

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BlueJ HelloWorld N timespublic 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"); }

}

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No { } in for-loop in HelloN

Why? A: Because loop covers one next statement y default

Let us add { }: where? Is there any difference

between before and after “ok”?A: Yes, there is. If after, HW and ok alternate in

the out-print.

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Three branching structures

(1) Do under a condition; otherwise do nothing [if… structure]

if(BooleanExpr) Statement orif(BooleanExpr) {Statements}

(2) Do under a condition; otherwise do differently [if…else… structure]

if(BooleanExpr)

{Statements1}

else

{Statements2}

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Java branching structure (3):

(3) Several conditions to do differently [if…else if… … else if… else structure]

if(BoolExpr1) Statement1;

else if(BoolExpr2)\\and not BoolExpr1

Statement2;else \\ (not BoolExpr1) and (not BoolExpr2)

Statement3;• Note NO Bool. Exp at else

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If/else example• Ticket’s price is £5, 60+ concession £3, children

12 or less go for free• Need a variable for the age, say YourAge, and

the price, say Price;• The fragment can be as:

if (YourAge<=12) Price=0;

else if (YourAge<=60) Price=5;

else //note NO CONDITION here

Price=3;

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Statements

• Assignment (followed by ;)• Method call (followed by ;)• if/ifelse/else (block, no ;)• for/while loop (block, no ;)• break (followed by ;)

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This is what was covered tonight

• Arithmetic expression and precedence

• Casting• Boolean expression• Statement• Loop for• Loop while• Choice structure if/elseif/else