SOFTWARE AND PROGRAMMING 1

SOFTWARE 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: [email protected]

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

Instructor: Mrs Jenny HuSCSIS, room NG26, tel. 020 7631 6726E-mail: [email protected]

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

Instructor: Prof. Boris MirkinSCSIS, room 111, tel. 020 7631 6746E-mail: [email protected]

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Subjects

• TicketMachine• TextIO and Scanner class to key in

data• String class• Math class

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Test1 8/2/6 awareness

Test1 will be carried out in MB33 during the lecture time (not lab time) from 7:30, 8/2/06

Subjects:• Variable: type, declaration, initialisation• Expression: arithmetic, Boolean• Loop for• Loop while• if( )… else if( ) ... else• Simple method

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What we want of a Ticket Machine

TicketMachine code: to model a ticket machine that issues flat-fare tickets.

The functionality: - accepting fare - calculating the amount to pay back- calculating the cumulative pay- issuing tickets- informing of the price and accumulated

payInstances may have different prices

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Coding Ticket MachinePrinciple: EACH function should be done with a specific

variable/method

Functions:

- differing instances (constructor)

- different pricing (var: price)

- accepting fare (var: balance)- calculating the cumulative pay (var: total)- calculating the money back (diff = balance-price)- issuing tickets (method for printing a ticket)- informing of the price and accumulated pay (methods for

each)

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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; } public int getTotal() { return total; } // 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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Example of branching(1)Problem: calculate income taxAlgorithm (Input: Income, Output: Tax):When the salary is less than 10000,

there is no tax. The tax is 15% on the amount earned

over 10000 up to 50000. Any money earned over 50000 are taxed

at 40%, that is, they pay 6000, the tax at 50000, plus the 40% added from the earnings over 50000.

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Example of branching(2)If()… :

  int Salary; int Tax=0; TextIO.putln("Input your salary "); Salary=TextIO.getInt(); //TextIO – a class

to be // put into the class’

directory 

if ((Salary > 10000)&&(Salary<=50000)) Tax=(Salary-10000)*15/100; if (Salary>50000) Tax=(Salary-50000)*40/100 + 6000;

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Example of branching(3)If()…else if()…else (preferable):  int Salary; int Tax;   if (Salary<=10000)              Tax=0;    else if (Salary<=50000)              Tax=(Salary-10000)*15/100;    else              Tax=(Salary-50000)*40/100 +

6000; • Q: What this would produce for Salary=15777?

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Method for Tax calculationMethod TC with input/parameter – Salary; output

- Tax  public float TC(int Salary) { float Tax;   if (Salary<=10000)              Tax=0;    else if (Salary<=50000)              Tax=(Salary-10000)*15/100;    else              Tax=(Salary-50000)*40/100 + 6000;  return Tax;}

Application:int mywages=15777;float mytax=TC(mywages); // would assign 866.55 to mytax

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Input/Output TextIO classTextIO.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.

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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 = uInputuInput; //why product?   System.out.print("The square is

"+Squared);           } // end of main()    } //end of class PrintSquare

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Input/Output TextIO class (3)

Other TextIO methods:b = TextIO.getByte(); // value read is a bytei = TextIO.getShort(); // value read is a shortj = TextIO.getInt(); // value read is an intk = TextIO.getLong(); // value read is a longx = TextIO.getFloat(); // value read is a floaty = TextIO.getDouble(); // value read is a doublea = TextIO.getBoolean(); // value read is a booleanc = TextIO.getChar(); // value read is a charw = TextIO.getWord(); // value read is a Strings = TextIO.getln(); // value read is a String

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Input with Scanner in JavaThe 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

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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 - declare an instance of Scanner - use it for prompting the user to

key in data (of a specified data type, preferably int or double or String) with a method: nextInt() or nextDouble() or next()

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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 (ik=0; ik<num; ik++) System.out.print(‘.’); System.out.println(); } \\end of main } \\end of class

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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

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Strings(1)

Declaring a String Object

String variable

•      An object of the class String

–    The class String is defined in java.lang.String and is automatically imported into every program

     Create a String object by using the keyword new and the String constructor method

•      String aGreeting = new String(“Hello”);

or String aGreeting = “Hello”;

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Strings(2)

Comparing String Values•     Strings are never actually changed; instead new Strings are

created and String variables hold the new addresses; A part of the Java system called the garbage collector will discard the unused strings

•     It is impossible to make a simple comparison of Strings; thus a number of methods are:

–   equals() method  if s1 and s2 are declared and initialised as

String: s1.equals(s2) true if s1 and s2 are exactly

the same sequences of characters NEVER s1==s2 !!! This is wrong, == applies

to numbers only.

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Strings(3)

Comparing String Values

•   Try  "HaHaHa ” "haHaHa" (2 differences)

s1.length() number of characters in s1 

•      charAt() method requires an integer argument which indicates the position of the character that the method returns

  s1.charAt(N) N-th character in s1(starting from N=0) String ss= “Look at you!”; What is ss.charAt(3)? ss.charAt(7)?

ss.charAt(17)?[In respect, ‘k’, ‘ ’ , and error]

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Strings(4)

  s1.substring(N,M) part of s1 in positions N, N+1, ..., M-1 (positions are numbered from 0)

String ss= “Look at you!”; What is ss.substring(3,7)?

Concatenation

    Concatenation - Joining strings, can be done with symbol +

      “45” + “36” = “4536”  

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Class MathMath.pi =3.14…, the ratio of the circumference to its diameter Math.abs(a) a if a >= 0, or -a if a < 0 Math.log(a) the natural logarithm (base e) of a Math.sqrt(a) square root of a Math.pow(a,b) ab , if b is integer then ab =aa…a (b times) 

  Math.random() pseudorandom number: double within interval [0.0, 1.0) (zero included, unity not) How to use it to generate a random integer between 1 and 6 (inclusive), to mimic casting a dice? double aa=Math.random();//aa, a real number between 0 and 1int an= 6*aa; //a real number between 0 and 6int rand=(int) an; // whole number between 0 and 5int randw=rand+1;// whole number betw. 1 and 6 Casting in Java: converting from higher number types to lower types int randw= (int) (6*Math.random()+1); How to generate a random integer between 10 and 20 inclusive? Answer:int rdt= (int) (11*Math.random()+10); 

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Math.random()pseudorandom number: double

within interval [0.0, 1.0) (zero included, unity not)

How to use it to generate a random integer between 1 and 6 (inclusive), to imitate casting a dice?

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Casting a dicedouble aa=Math.random();

//aa, a real number between 0 and 1int an= 6*aa; //a real number between 0

and 6int rand=(int) an;

// whole number between 0 and 5int randw=rand+1;

// whole number between 1 and 6 The same in one line:int randw= (int) (6*Math.random()+1); 

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Casting a dice questionHow to generate a random integer

between 10 and 20 inclusive? Answer:int rdt= (int) (11*Math.random()+10);