lec2 programming

8/11/2019 lec2 programming

1/20

OOD Identifying Classes

Identifying the nouns (and noun phrases) in the

application description

The attributes correspond to descriptive words

The behavior corresponds topublic methods

contained in their corresponding classes

Occasionally classes are not build to generate

objects but to collect static methods and constants. Utility classes, e.g.,Math, Color, Integer

Create classes which represent a single concept


2/20

class Purse {

public Purse();

public void addNickels(int count);public addDimes(int count);

public addQuarters(int count);

public double getTotal();

}

class Coin{

public Coin(double value, String aName);

public double getValue();}

class Purse {

public Purse();

public void add(Coin aCoin);

public double getTotal();

}

Two concepts:

1. a purse that holds coins,

and

2. the value of each coin.

Class Purse uses/depends on

class Coin


3/20

Case Study: Invoices

Write a set of classes to support the creation and

printing of invoices

Classes:

Invoice

Product

LineItem

Address


4/20

public class Product {

public Product(String aDescription, double aPrice) {

description = aDescription;

price = aPrice;}

public String getDescription() {

return description;

}

public double getPrice() {

return price;

}

private String description;

private double price;

}

public class LineItem{

public LineItem(Product aProduct, int aQuantity) {

theProduct = aProduct;

quantity = aQuantity;

}

public double getTotalPrice() {

return theProduct.getPrice() * quantity;

}

public String format() {return String.format("%-30s%8.2f%5d%8.2f",

theProduct.getDescription(), theProduct.getPrice()

, quantity, getTotalPrice());

}

private int quantity;

private Product theProduct;}

Product and LineItem

classes


5/20

public class Address{

public Address(String aName, String aStreet,

String aCity, String aState, String aZip) {

name = aName;

street = aStreet;

city = aCity;

state = aState;

zip = aZip;

}

public String format() {

return name + "\n" + street + "\n"

+ city + ", " + state + " " + zip;

}

private String name;private String street;

private String city;

private String state;

private String zip;

}

Address class


6/20

public class Invoice{

public Invoice(Address anAddress) {

items = new ArrayList();

billingAddress = anAddress;

}public void add(Product aProduct, int quantity) {

LineItem anItem = new LineItem(aProduct, quantity);

items.add(anItem);

}

public String format()

{

String r = " I N V O I C E\n\n"+ billingAddress.format()

+ String.format("\n\n%-30s%8s%5s%8s\n",

"Description", "Price", "Qty", "Total");

for (LineItem i : items) {

r = r + i.format() + "\n";

}

r = r + String.format("\nAMOUNT DUE: $%8.2f", getAmountDue());

return r;

}

public double getAmountDue() {

double amountDue = 0;

for (LineItem i : items) {

amountDue = amountDue + i.getTotalPrice();

}

return amountDue;

}

private Address billingAddress;

private ArrayList items;

}

Invoice class


7/20

public class InvoiceTester{

public static void main(String[] args) {

Address samsAddress

= new Address("Sam's Small Appliances",

"100 Main Street", "Anytown", "CA", "98765");

Invoice samsInvoice = new Invoice(samsAddress);

samsInvoice.add(new Product("Toaster", 29.95), 3);

samsInvoice.add(new Product("Hair dryer", 24.95), 1);

samsInvoice.add(new Product("Car vacuum", 19.99), 2);

System.out.println(samsInvoice.format());}

}

InvoiceTester


8/20

UML

Universal Modeling Language (UML) a standard language for specifying, visualizing, constructing,

and documenting the artifacts of software systems, as well asfor business modeling and other non-software systems.

Class diagram a type of static structure diagram that describes the

structure of a system class name, attributes, methods

relationship between classes

Object diagram shows the snapshot of a modeled system, at a specific point

in time

Not required


9/20

A Case Study

An Application Centre for university admissions

A student can choose 3 different universities, and

lets assume that this center will accept up to 100

different applications.

This program has to allow the user to:

enter the student applications,

accept students in some of the universities that they chose,

display the status of the applications.


10/20

Class Candidates Based on Nouns

Application Centre

University Admissions

Student

Universities

Applications Status of Applications

Two classes: ApplicationCentre and

StudentApplication

Too simple to constitute

separate classes

Should be a property


11/20

UML Class Diagram

Application Centre

- st[100]: StudentApplication

- name : String

+ addStudent(): boolean

+ getStudent(int): StudentApplication

StudentApplication

- name: String

- univ1, univ2, univ3: String

- acc1, acc2, acc3: boolean

+ setAcceptance(): void

+ toString(): String

*1


12/20

1. class StudentApplication{2. private String name;3. private String university0;4. private String university1;5. private String university2;6. private boolean accept0;7. private boolean accept1;8. private boolean accept2;9. public StudentApplication (String n, String u0, String u1, String u2){10. name = n;11. university0=u0;12. university1=u1;

13. university2=u2;14. accept0=accept1=accept2=false;15. }16. public void setAcceptance(int which, boolean decision){17. switch(which){18. case 0: accept0=decision; break;19. case 1: accept1=decision; break;20. case 2: accept2=decision; break;

21. }22. }23. public String toString(){24. String result = name + ":\n";25. result += university0;26. if (accept0) result += " - accepted\n";27. else result += " - rejected\n";28. result += university1;

29. if (accept1) result += " - accepted\n";30. else result += " - rejected\n";31. result += university2;32. if (accept2) result += " - accepted\n";33. else result += " - rejected\n";34. return result;35. }36. }


13/20

1. class ApplicationCentre {

2. private String name;

3. private StudentApplication[] st;

4. private int studentCount;5. private int size;

6.

7. public ApplicationCentre(String s){

8. name=s;

9. size=100;

10. st = new StudentApplication[size];

11. studentCount=0;

12. }

13. public String getName() {

14. return name;

15. }

16. public boolean addStudent(StudentApplication s){

17. if (studentCount==size) return false;

18. st[studentCount]=s;

19. studentCount ++;20. return true;

21. }

22. public StudentApplication getStudent(int which){

23. if ( which < 0 || which > studentCount-1){

24. return null;

25. }

26. return st[which];

27. }

28.}


14/20

JOptionPane

a class in javax.swing

Method Name Description

showConfirmDialog Asks a confirming question, like yes/no/cancel.

showInputDialog Prompt for some input.

showMessageDialog Tell the user about something that has happened.

showOptionDialog The Grand Unification of the above three.


15/20

1. import javax.swing.JOptionPane;

2. public class Applications {

3. public static void main( String args[] ) {

4. ApplicationCentre appCentre= new ApplicationCentre (OUAC");

5. String stopper="quit";6. int nrStud=0;

7. JOptionPane.showMessageDialog(null,"Enter student names, each followed by 3 choices

8. of universities. To stop enter for name the word quit","Input", JOptionPane.PLAIN_MESSAGE);

9. String n = JOptionPane.showInputDialog("Student's name ?");

10. boolean flag = true;

11. while ( !n.equals(stopper) && flag){

12. String u1 = JOptionPane.showInputDialog("1st university ?");

13. String u2 = JOptionPane.showInputDialog("2nd university ?");

14. String u3 = JOptionPane.showInputDialog("3rd university ? ");15. StudentApplication s=new StudentApplication (n, u1, u2, u3);

16. flag = appCentre.addStudent(s);

17. n = JOptionPane.showInputDialog("Student's name ?");

18. nrStud++;

19. }

20.

21. String line = JOptionPane.showInputDialog(" Indicate which applications are to be

22. accepted by entering the student index number. To stop enter for name the word quit");

23. while (!line.equals(stopper)) {24. int stnr = Integer.parseInt(line);

25. line = JOptionPane.showInputDialog("Enter university index 0..2");

26. int anr = Integer.parseInt(line);

27. appCentre.getStudent(stnr).setAcceptance(anr, true);

28. line= JOptionPane.showInputDialog(" Indicate which applications are to be accepted by

29. entering the student index number. To stop enter for name the word quit");

30. }

31.

32. JOptionPane.showMessageDialog(null, " Records for all applicants to "+ appCentre.getName() +33. "\n","Records", JOptionPane.PLAIN_MESSAGE);

34. for (int i = 0; i < nrStud; i++)

35. JOptionPane.showMessageDialog(null,appCentre.getStudent(i).toString() ,"Records",

36. JOptionPane.PLAIN_MESSAGE);

37. }

38.}


16/20

Arrays

Related data items of same type

Group of contiguous memory locations Each memory location has same name

Each memory location has same type


17/20

A 12-element array

-45

6

0

72

1543

-89

0

62

-3

1

6453

78

c[ 1 ]

c[ 2 ]

c[ 4 ]

c[ 3 ]

c[ 5 ]

c[ 6 ]

c[ 7 ]

c[ 8 ]

c[ 9 ]

c[ 10 ]

c[ 11 ]

c[ 0 ]Name of array (Notethat all elements of

this array have thesame name, c)

Position number (index

of subscript) of theelement within array c


18/20

Declaring and Allocating Arrays

Declaring and allocating arrays

Arrays are objects that occupy memory

Allocated dynamically with operator newint c[] = new int[ 12 ];

Equivalent to

int c[]; // declare array

c = new int[ 12 ]; // allocate array We can allocate arrays of objects too

String b[] = new String[ 100 ];

Obtaining the size of an array c.length


19/20

Initializing Arrays

Initialize array elements

Use initializer list

Items enclosed in braces ({}) Items in list separated by commas

int n[] = { 10, 20, 30, 40, 50 };

Creates a five-element array

Subscripts of 0, 1, 2, 3, 4

Do not need operator new


20/20

Arrays of Objects

Allocating memory for an array does not

automatically allocate the memory for each

element! Only references to the elements are created

The objects need to be allocated separately

ExampleAccount accounts[] = new Account[12];

accounts[0].getBalance(); // wrong, Account[0] is not initialized

Account accounts[] = new Account[12];

for (int i = 0; i < accounts.length; i++)

accounts[i] = new Account(); // initializing the array elements

accounts[0].getBalance(); // correct

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lec2 programming

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