SOFTWARE AND PROGRAMMING 1

SOFTWARE AND PROGRAMMING 1 Advert: NO TEST1 on 7/02: TEST1 will be 14/02 Lab: SH131, BBK536 6:00-7:30 (from 24.01.07) [each student must have obtained access to Birkbeck computing, and those whose surnames start with A-L, to SCSIS computing too] Lecture: Gor B4 7:40-9:00 (from 24.01.07) Lab SH131: students whose family names (surnames) begin A-L Instructor: Ms Marie-Helene Ng SCSIS, 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 Mirkin

Webpages The course web page webct.bbk.ac.uk is used for announcements and assignments. Those who have problems with accessing the course module should contact Marie-Helene (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

Test1 14/2/7 awareness Open-book in-class Test1 14/2/7 subjects: • Variable: type, declaration, initialisation • Expression • Loop for • Loop while • if( )… else if( ) ... else • Method

Contents • Leftovers (conditional operator) • Ticket Machine • Method; Accessor, Mutator • Double loop • Input data from keyboard: TextIO, Scanner

Precedence table

Conditional operator • Used for assigning a value depending on a condition: A= Condition ? ResultIfTrue :ResultIfFalse Example: int b=2; int c= 7; int A=(b < c) ? b : c; %put min(b,c) into A How this can be done with if/else: int b=2; int c= 7; int A; if (b<c) {A=b;} else {A=c;}

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

Ticket Machine (2) // TicketMachine’s continuation public 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

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

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?

Questions • How many methods are in TicketMachine? - five • If there is any syntactic difference between a method and constructor? – two: absence of the output type, compulsory name • Which of the methods are accessors and which are mutators? - Two in the beginning are accessors, three in the end are mutators

Accessor methods • Accessors provide information about the state of an object. • Methods have a structure consisting of a header and a body. • The header defines the method’s signature. public int getPrice() • The body encloses the method’s statements.

Accessor methods return type visibility modifier method name parameter list (empty) public int getPrice() { return price; } return statement start and end of method body (block)

Mutator methods • Have a similar method structure: header and body. • Used to mutate (i.e. change) an object’s state. • Achieved through changing the value of one or more fields. • Typically contain assignment statements. • Typically receive parameters.

Mutator methods return type (void) visibility modifier method name parameter public void insertMoney(int amount) { balance = balance + amount; } field being changed assignment statement

Printing method public void printTicket() { // Simulate the printing of a ticket. System.out.println("##################"); System.out.println("# The BlueJ Line"); System.out.println("# Ticket"); System.out.println("# " + price + " cents."); System.out.println("##################"); System.out.println(); // Update the total collected with the balance. total = total + balance; // Clear the balance. balance = 0; }

Passing data via parameters

Double loop (1) class AddTable { public static void main(String[ ] args){ int sum; for (int ite1=1;ite1<3; ite1++) {//loop1 for (int ite2=1;ite2<5; ite2++) {//loop2 sum=ite1+ite2; System.out.print(sum +" ");}//loop2 System.out.println();}//loop1 } //method main ends } //class ends

Double loop (2) This prints 2 3 4 5 3 4 5 6 Why? A better printing ? Such as: Addition Table + 1 2 3 4 1 2 3 4 5 2 3 4 5 6

Double loop (3) class AddTable { public static void main (String[] args) {int sum; for (int i1=1;i1<3; i1++){ System.out.print(i1 + " ! "); for (int i2=1;i2<5; i2++){ sum=i1+i2; System.out.print(sum +" ");} System.out.println();} } }

Double loop (4): with method class AddTableMeth { public static void main (String[] args) { PrintTable(2,4); }\\end main public static PrinTable(int rowsize, int columnsize){ for (int i1=1;i1<rowsize+1; i1++){ System.out.print(i1 + " ! "); for (int i2=1;i2<columnsize+1; i2++){ sum=i1+i2; System.out.print(sum +" ");} System.out.println();} } }\\end class

Double loop (5) produces 1! 2 3 4 5 2! 3 4 5 6 3! 4 5 6 7 Q: How to make it look better? (See printing method in TicketMachine.) Q: How to modify it to other ranges? Q: Make a MULTIPLICATION TABLE?

Input/Output TextIO class TextIO.java, added to the directory that contains your class, eases input of data from the keyboard To input an integer: int UsInput = TextIO.getInt(); Computer will wait for the user to type in an integer value to UsInput.

Input/Output TextIO class (2) public class PrintSquare { public static void main(String[] args) { int uInput; // the number to be input by the user int Squared; // the userInput, multiplied by itself System.out.print("Please type a number: "); uInput = TextIO.getInt(); Squared = uInputuInput; //why product? System.out.print("The square is "+Squared); }// end of main() } //end of class PrintSquare

Input/Output TextIO class (3) Other TextIO methods: b = TextIO.getByte(); // value read is a byte i = TextIO.getShort(); // value read is a short j = TextIO.getInt(); // value read is an int k = TextIO.getLong(); // value read is a long x = TextIO.getFloat(); // value read is a float y = TextIO.getDouble(); // value read is a double a = TextIO.getBoolean(); // value read is a boolean c = TextIO.getChar(); // value read is a char w = TextIO.getWord(); // value read is a String s = TextIO.getln(); // value read is a String

Input/Output in Java The TextIO class contains static member methods TextIO.put() and TextIO.putln(), the same as System.out.print() and System.out.println(). TextIO can only be used in a program if TextIO is available to that program. It is not built into Java. From Java 1.5.0 version on, there is a similar class in Systems.in: Scanner

Input with Scanner class(1) From Java 1.5.0 version on, there is a similar class in System.in. Scanner(System.in): - import the java.util package in a line preceding the class, - then declare an instance of Scanner and - then use it for prompting the user to enter data (of a specified data type, preferably int or double) from keyboard

Input with Scanner class (2) import java.util.* class PrintDot{ int num=0; public static void main(String[ ] args){ Scanner scap = new Scanner(System.in); System.out.println(“How many dots to print? “); num=scap.nextInt(); for (int ik=0; ik<num; ik++) System.out.print(‘.’); System.out.println(); } \\end of main } \\end of class

Using method with Scanner import java.util.* class PrintDot{ int number=0; public static void main(String[ ] args){ Scanner scap = new Scanner(System.in); System.out.println(“How many ampersands to print? “); number=scap.nextInt(); ppp(number); }\\end of main void ppp(nnn) { for (ik=0; ik<nnn; ik++) System.out.print(‘&’); System.out.println(); } \\end of ppp } \\end of class

SOFTWARE AND PROGRAMMING 1