SFTWARE AND PROGRAMMING 1

Lecture: MB33 7:30-9:00 (except 11&18.01.06)Lab: B43, MB321, MB536 6:00-7:30 (from

25.01.05)[each student must have obtained access to Birkbeck

computing]

Lab MB536: students whose family names fall in A-FInstructor:Mr Zheng ZhuLKL, tel. 020 7763 2115 E-mail: zheng@dcs.bbk.ac.uk

Lab G03 Clore Centre: students whose family names fall in G-Ka

Instructor: Mrs Jenny HuSCSIS, room NG26, tel. 020 7631 6726E-mail: jennychhu@yahoo.com

Lab 12 Gordon Sq. 43: students whose family names fall in Ke -Y

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

O

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Webpages

The course web page

webct.bbk.ac.uk

is used for announcements and assignments. To have access, ALL must submit their login to Marie-Helen (marie-helene@dcs.bbk.ac.uk)An open-to-all web-site with lecture notes, schedule and files:www.dcs.bbk.ac.uk/~mirkin/sp105

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Test1 8/2/6 awareness

Test1 subjects:• Variable: type, declaration,

initialisation• Expression• Loop for• Loop while• if( )… else if( ) ... else• Simple class structure• Simple method

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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 public void prrt() \\printing number times { for(int i=1;i<=number;i++) \\loop go(); System.out.println("ok"); }

}

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Precedence in arithmetic expressions

•  /, %, and * first, then + and –:2 * 6 / 4 + 5 – 2 * 3 = 3 + 5 – 6 = 2

(here are integers only)

• To change this or if not sure, use ( ): 2 * 6.0 / (4 + 5) – 2 * 3 = 12.0/9 – 6 = –

4.67 (reals are here because of 6.0)2 * 6 / 4 + (5 – 2) * 3 = 12 whereas2 * 6 / 4 + 5 – 2 * 3 = 2

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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:

• float weeklybudget = (float) bankbalance /4;

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Boolean expressions

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Precedence table

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Ticket Machine (1)/* * TicketMachine models a ticket machine that issues * flat-fare tickets. */public class TicketMachine{private int price;private int balance;private int total;

public TicketMachine(int ticketCost) //constructor { price = ticketCost; balance = 0; total = 0; } public int getPrice() { return price; } public int getBalance() { return balance; }

// see next page for continuation

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Ticket Machine (2)// TicketMachine’s continuationpublic void insertMoney(int amount) { if(amount > 0) balance = balance + amount; else { System.out.println("Use a positive amount: " + amount); } } public int refundBalance() { int amountToRefund; amountToRefund = balance; balance = 0; return amountToRefund; }// continued on the next page

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Ticket Machine (3)// TicketMachine’s end public void printTicket() { if(balance >= price) { // Simulate the printing of a ticket. System.out.println("##################"); System.out.println("# The BlueJ Line"); System.out.println("# Ticket"); System.out.println("# " + price + " pence."); System.out.println("##################"); System.out.println();

total = total + price; // Update the total balance = balance - price; // Update the balance } else { System.out.println("You must insert at least: " + (price - balance) + " more pence."); } } }//end of class

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A comment

I consider printTicket()method as somewhat inconsistent:

printing (an accessing activity) is mixed up with

changing the balance and total (mutating activities)

Any suggestions?

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Questions

• How many methods are in TicketMachine?

• If there is any syntactic difference between a method and constructor (in BlueJ)?

• Which of the methods are accessors and which are mutators?

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Loop forfor(int var=1;var<=st;var++){do operation

depending on var}

• var++ is var=var+1;• 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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Loop while for(init; test; update){ statements }All 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; while(test){ statements;

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

test condition (not necessarily involving the counter!), and update – in a different structure

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Example:

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

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

if (K < 7)

{ break; } //what is “break”?

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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Java branching structure (1,2):

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

if(BooleanExpr) Statement or if(BooleanExpr) {Statements}(2) Do under a condition;

otherwise do differently [if…else… structure]

if(BooleanExpr) Statement1;

elseStatement2;

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Java branching structure (3):

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

if(BooleanExpr1) Statement1;

else if(BooleanExpr2)Statement2;

elseStatement3;

• 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;