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MSc IT
Programming Methodology (2)
Oblong
EasyScanner
BankAccount
Implementing Classes
Learning objectives
• design classes using the notation of the Unified Modelling Language (UML);
• write the Java code for a specified class;
• explain the difference between public and private access to attributes and methods;
• explain the use of the static keyword;
• pass objects as parameters.
Structured programming…
// switch on light
// get building
// check if passed
main
boolean light;
int mark;
String roomNumber;
Object-oriented programming…
String roomNumber;
int mark;
// switch on light
// get building
// check if passed
Room Student Projector
boolean light;
Looking inside a class….
Student
data
Student
name
number
marks
Student
data
name
number
marks
Student
data methods
name
number
marks
Student
data methods
getName
getNumber
setMarks
Student
Oblong
Oblong
data
Oblong
data
length
height
Oblong
data
length
height
methods
Oblong
data
length
height
methods
getLength
calculateArea
Oblong
The notation of the
Unified Modelling Language (UML)
Oblong
length height
Oblong( )
setLength( )
setHeight( )
getLength( )
getHeight( )
calculateArea( )
calculatePerimeter( )
Class Name
data
methods
attributes
Oblong
length : ? height : ?
Oblong( ? )
setLength( ? ): ?
setHeight( ? ): ?
getLength( ? ): ?
getHeight( ? ): ?
calculateArea( ? ): ?
calculatePerimeter( ? ): ?
Oblong
length : double height : ?
Oblong( ? )
setLength( ? ): ?
setHeight( ? ): ?
getLength( ? ): ?
getHeight( ? ): ?
calculateArea( ? ): ?
calculatePerimeter( ? ): ?
Oblong
length : double height : double
Oblong( ? )
setLength( ? ): ?
setHeight( ? ): ?
getLength( ? ): ?
getHeight( ? ): ?
calculateArea( ? ): ?
calculatePerimeter( ? ): ?
Oblong
length : double height : double
Oblong( double, double )
setLength( ? ): ?
setHeight( ? ): ?
getLength( ? ): ?
getHeight( ? ): ?
calculateArea( ? ): ?
calculatePerimeter( ? ): ?
Oblong
length : double height : double
Oblong( double, double )
setLength( double )
setHeight( ? ): ?
getLength( ? ): ?
getHeight( ? ): ?
calculateArea( ? ): ?
calculatePerimeter( ? ): ?
Oblong
length : double height : double
Oblong( double, double )
setLength( double )
setHeight( double )
getLength( ? ): ?
getHeight( ? ): ?
calculateArea( ? ): ?
calculatePerimeter( ? ): ?
Oblong
length : double height : double
Oblong( double, double )
setLength( double )
setHeight( double )
getLength( ): double
getHeight( ? ): ?
calculateArea( ? ): ?
calculatePerimeter( ? ): ?
Oblong
length : double height : double
Oblong( double, double )
setLength( double )
setHeight( double )
getLength( ): double
getHeight( ): double
calculateArea( ? ): ?
calculatePerimeter( ? ): ?
Oblong
length : double height : double
Oblong( double, double )
setLength( double )
setHeight( double )
getLength( ): double
getHeight( ): double
calculateArea( ): double
calculatePerimeter( ? ): ?
Oblong
length : double height : double
Oblong( double, double )
setLength( double )
setHeight( double )
getLength( ): double
getHeight( ): double
calculateArea( ): double
calculatePerimeter( ): double
Oblong
length : double height : double
Oblong( double, double )
setLength( double )
setHeight( double )
getLength( ): double
getHeight( ): double
calculateArea( ): double
calculatePerimeter( ): double
public class Oblong
{
// attributes
// methods
}
public class Oblong
{
}
double length; double height;
Attributes declared outside of any methods
public class Oblong
{
}
double length; double height;
public class Oblong
{
}
double length; double height;
Attributes should be hidden inside the class
public class Oblong
{
}
double length; double height;
privateprivate
Implementing the Oblong methods…
public class Oblong
{
}
double length; double height;
privateprivate
Oblong ob1 = new Oblong (12.5, 7.5);
public class Oblong
{
}
double length; double height;
privateprivate
Oblong ob1 = new Oblong (12.5, 7.5);
Oblong(double ?, double ?) {
}
// more methods here
public class Oblong
{
}
double length; double height;
privateprivate
Oblong ob1 = new Oblong (12.5, 7.5);
Oblong(double ?, double ?) {
}
// more methods here
Methods should be visible outside of the class
public class Oblong
{
}
double length; double height;
privateprivate
Oblong ob1 = new Oblong (12.5, 7.5);
Oblong(double ?, double ?) {
}
// more methods here
Methods should be visible outside of the class
public
public class Oblong
{
}
double length; double height;
privateprivate
Oblong ob1 = new Oblong (12.5, 7.5);
Oblong(double ?, double ?) {
}
// more methods here
public
A constructor has no return type
public class Oblong
{
}
double length; double height;
privateprivate
Oblong ob1 = new Oblong (12.5, 7.5);
Oblong(double ?, double ?) {
}
// more methods here
public
public class Oblong
{
}
double length; double height;
privateprivate
Oblong ob1 = new Oblong (12.5, 7.5);
Oblong(double lengthIn, double ?) {
}
// more methods here
public
public class Oblong
{
}
double length; double height;
privateprivate
Oblong ob1 = new Oblong (12.5, 7.5);
Oblong(double lengthIn, double ?) {
}
// more methods here
public
public class Oblong
{
}
double length; double height;
privateprivate
Oblong ob1 = new Oblong (12.5, 7.5);
Oblong(double lengthIn, double heightIn)
{
}
// more methods here
public
public class Oblong
{
}
double length; double height;
privateprivate
Oblong ob1 = new Oblong (12.5, 7.5);
Oblong(double lengthIn, double heightIn)
{
// set the values of length and height}
// more methods here
public
public class Oblong
{
}
double length; double height;
privateprivate
Oblong ob1 = new Oblong (12.5, 7.5);
Oblong(double lengthIn, double heightIn)
{
// set the values of length and height}
// more methods here
public
public class Oblong
{
}
double length; double height;
privateprivate
Oblong ob1 = new Oblong (12.5, 7.5);
Oblong(double lengthIn, double heightIn)
{ length = lengthIn;
}
// more methods here
public
public class Oblong
{
}
double length; double height;
privateprivate
Oblong ob1 = new Oblong (12.5, 7.5);
Oblong(double lengthIn, double heightIn)
{ length = lengthIn;
height = heightIn;}
// more methods here
public
What happens if you don’t write a constructor?
A default constructor is added for you!
public class Oblong
{
}
double length; double height;
privateprivate
Oblong(){
}
public
// more methods here
public class Oblong
{
}
double length; double height;
privateprivate
Oblong(){
}
public
// more methods here
A default constructor has no code inside it.
public class Oblong
{
}
double length; double height;
privateprivate
Oblong(){
}
public
// more methods here
Oblong ob1 = new Oblong ( );
public class Oblong
{
}
double length; double height;
privateprivate
Oblong(){
}
public
// more methods here
Oblong ob1 = new Oblong (12.5, 7.5);
public class Oblong
{
}
double length; double height;
privateprivate
Oblong ob1 = new Oblong (12.5, 7.5);
public class Oblong
{
}
double length; double height;
privateprivate
public Oblong(double lengthIn, double heightIn)
{
}
// more methods here
length = lengthIn;
height = heightIn;
Oblong ob1 = new Oblong (12.5, 7.5);
public class Oblong
{
}
double length; double height;
privateprivate
System.out.println( ob1.getLength() );
getLength(){ }
public double
return length;
// more methods here
public class Oblong
{
}
double length; double height;
privateprivate
System.out.println( ob1.getHeight() );
getHeight(){ }
public double
return height;
// more methods here
public class Oblong
{
}
double length; double height;
privateprivate
ob1.setLength( 14.75);
setLength( double ?){ }
public
// more methods here
public class Oblong
{
}
double length; double height;
privateprivate
ob1.setLength( 14.75);
setLength( double ?){ }
public
// more methods here
void
public class Oblong
{
}
double length; double height;
privateprivate
ob1.setLength( 14.75);
setLength( double ?){ }
public
// more methods here
void
public class Oblong
{
}
double length; double height;
privateprivate
ob1.setLength( 14.75);
setLength( double lengthIn){ }
public
// more methods here
void
public class Oblong
{
}
double length; double height;
privateprivate
ob1.setLength( 14.75);
setLength( double lengthIn){ // reset length}
public
// more methods here
void
public class Oblong
{
}
double length; double height;
privateprivate
ob1.setLength( 14.75);
setLength( double lengthIn){ }
public void
length = lengthIn;
// more methods here
public class Oblong
{
}
double length; double height;
privateprivate
ob1.setHeight( 5.9 );
// more methods here
public class Oblong
{
}
double length; double height;
privateprivate
ob1.setHeight( 5.9 );
setHeight( double heightIn){ }
public void
height = heightIn;
// more methods here
public class Oblong
{
}
double length; double height;
privateprivate
System.out.println( ob1.calculateArea() );
// more methods here
public class Oblong
{
}
double length; double height;
privateprivate
System.out.println( ob1.calculateArea() );
// more methods here
calculateArea(){ }
public double
return length * height;
public class Oblong
{
}
double length; double height;
privateprivate
System.out.println( ob1.calculatePerimeter());
// more methods here
public class Oblong
{
}
double length; double height;
privateprivate
System.out.println( ob1.calculatePerimeter());
// more methods here
calculatePerimeter(){ }
public double
return 2 * (length + height);
The BankAccount class….
BankAccount
accountNumber : String
accountName : String
balance : double
BankAccount (String, String)
getAccountNumber() : String
getAccountName() : String
getBalance() : double
deposit(double)
withdraw(double)
public class BankAccount
{
private String accountNumber;
private String accountName;
private double balance;
}
public class BankAccount
{
private String accountNumber;
private String accountName;
private double balance;
}
public class BankAccount
{
private String accountNumber;
private String accountName;
private double balance;
}
public BankAccount(String numberIn, String nameIn)
{
accountNumber = numberIn;
accountName = nameIn;
balance = 0;
}
public class BankAccount
{
private String accountNumber;
private String accountName;
private double balance;
}
public String getAccountName()
{
return accountName;
}
public class BankAccount
{
private String accountNumber;
private String accountName;
private double balance;
}
public String getAccountNumber()
{
return accountNumber;
}
public class BankAccount
{
private String accountNumber;
private String accountName;
private double balance;
}
public String getABalance()
{
return balance;
}
public class BankAccount
{
private String accountNumber;
private String accountName;
private double balance;
}
public void deposit(double amountIn)
{
balance = balance + amountIn;
}
public class BankAccount
{
private String accountNumber;
private String accountName;
private double balance;
}
public void withdraw(double amountIn)
{
balance = balance – amountIn;
}
public class BankAccountTester
{
public static void main(String[ ] args)
{
BankAccount account1
= new BankAccount("99786754","Susan Richards");
account1.deposit(1000);
System.out.println("Account number: "
+ account1.getAccountNumber());
System.out.println("Account name: " +
account1.getAccountName());
System.out.println("Current balance: " + account1.getBalance());
}
}
Amending the BankAccount class…
“0012765” “Funmi Odulopo” £1200.49
“09887254” “Mary Stephenson” £975.12
“07721009” “Dilraj Mann” £3975.75
acc1
acc2
acc3
1.25%
1.25%
1.25%
acc1.getBalance();
acc1.getInterestRate();
acc2.addInterest ();
“0012765” “Funmi Odulopo” £1200.49
“09887254” “Mary Stephenson” £987.31
“07721009” “Dilraj Mann” £3975.75
acc1
acc2
acc3
1.25%
1.25%
1.25%
acc1.getBalance();
acc1.getInterestRate();
acc2.addInterest ();
“0012765” “Funmi Odulopo” £1200.49
“09887254” “Mary Stephenson” £987.31
“07721009” “Dilraj Mann” £3975.75
acc1
acc2
acc3
1.25%
1.25%
1.25%
acc1.getBalance();
acc1.getInterestRate();
acc2.addInterest ();
acc2.getInterestRate();
“0012765” “Funmi Odulopo” £1200.49
“09887254” “Mary Stephenson” £987.31
“07721009” “Dilraj Mann” £3975.75
acc1
acc2
acc3
1.25%
1.25%
1.25%
acc1.getBalance();
acc1.getInterestRate();
acc2.addInterest ();
acc2.getInterestRate();
acc3.deposit( 500 );
“0012765” “Funmi Odulopo” £1200.49
“09887254” “Mary Stephenson” £987.31
“07721009” “Dilraj Mann” £4475.75
acc1
acc2
acc3
1.25%
1.25%
1.25%
acc1.getBalance();
acc1.getInterestRate();
acc2.addInterest ();
acc2.getInterestRate();
acc3.deposit( 500 );
“0012765” “Funmi Odulopo” £1200.49
“09887254” “Mary Stephenson” £987.31
“07721009” “Dilraj Mann” £4475.75
acc1
acc2
acc3
1.25%
1.25%
1.25%
acc1.getBalance();
acc1.getInterestRate();
acc2.addInterest ();
acc2.getInterestRate();
acc3.deposit( 500 );
acc3.setInterestRate(1.5);
“0012765” “Funmi Odulopo” £1200.49
“09887254” “Mary Stephenson” £987.31
“07721009” “Dilraj Mann” £4475.75
acc1
acc2
acc3
1.25%
1.25%
1.5%
acc1.getBalance();
acc1.getInterestRate();
acc2.addInterest ();
acc2.getInterestRate();
acc3.deposit( 500 );
acc3.setInterestRate(1.5);
“0012765” “Funmi Odulopo” £1200.49
“09887254” “Mary Stephenson” £987.31
“07721009” “Dilraj Mann” £4475.75
acc1
acc2
acc3
acc1.getBalance();
acc1.getInterestRate();
acc2.addInterest ();
acc2.getInterestRate();
acc3.deposit( 500 );
acc3.setInterestRate(1.5);
1.5%
“0012765” “Funmi Odulopo” £1200.49
“09887254” “Mary Stephenson” £987.31
“07721009” “Dilraj Mann” £4475.75
acc1
acc2
acc3
1.5%
acc1.getBalance();
acc2.addInterest ();
acc3.deposit( 500 );
“0012765” “Funmi Odulopo” £1200.49
“09887254” “Mary Stephenson” £987.31
“07721009” “Dilraj Mann” £4475.75
acc1
acc2
acc3
1.5%
acc1.getBalance();
acc2.addInterest ();
acc3.deposit( 500 );
BankAccount.setInterestRate(1.4);
“0012765” “Funmi Odulopo” £1200.49
“09887254” “Mary Stephenson” £987.31
“07721009” “Dilraj Mann” £4475.75
acc1
acc2
acc3
1.4%
acc1.getBalance();
acc2.addInterest ();
acc3.deposit( 500 );
BankAccount.setInterestRate(1.4);
“0012765” “Funmi Odulopo” £1200.49
“09887254” “Mary Stephenson” £987.31
“07721009” “Dilraj Mann” £4475.75
acc1
acc2
acc3
1.4%
acc1.getBalance();
acc2.addInterest ();
acc3.deposit( 500 );
BankAccount.setInterestRate(1.4);
BankAccount.getInterestRate( );
“0012765” “Funmi Odulopo” £1200.49
“09887254” “Mary Stephenson” £987.31
“07721009” “Dilraj Mann” £4475.75
acc1
acc2
acc3
1.4%
acc1.getBalance();
acc2.addInterest ();
acc3.deposit( 500 );
BankAccount.setInterestRate(1.4);
BankAccount.getInterestRate( );
This is a class attribute.
“0012765” “Funmi Odulopo” £1200.49
“09887254” “Mary Stephenson” £987.31
“07721009” “Dilraj Mann” £4475.75
acc1
acc2
acc3
1.4%
acc1.getBalance();
acc2.addInterest ();
acc3.deposit( 500 );
BankAccount.setInterestRate(1.4);
BankAccount.getInterestRate( );
This is a class method.
How do we create class attributes and class methods?
Use the static keyword!
private static double interestRate;
public static void setInterestRate(double rateIn)
{
interestRate = rateIn;
}
public static double getInterestRate()
{
return interestRate;
}
public class BankAccount2{ // attributes and methods as before plus addInterest
}
The addInterest method ….
public class BankAccount2
{
private String accountNumber;
private String accountName;
private double balance;
}
private static double interestRate;
public void addInterest()
{
balance = balance + (balance * interestRate)/100;
}
The BankAccount2 constructor ?
public class BankAccount2
{
private String accountNumber;
private String accountName;
private double balance;
}
private static double interestRate;
public BankAccount2(String numberIn, String nameIn)
{
accountNumber = numberIn;
accountName = nameIn;
balance = 0;
}
What about the interestRate attribute?
Java does not give an initial value to local variables but does initialize attributes!
Initializing attributes
int
double
char
Objects0
boolean false null
public class BankAccount2
{
private String accountNumber;
private String accountName;
private double balance;
private static double interestRate ;
// methods here
}
= 0;
The EasyScanner class…
Remember how we used EasyScanner?
int x;
System.out.println(“Enter number”);
X = EasyScanner.nextInt() ;
This must be a class method!
import java.util.*;
public class EasyScanner
{
public static int nextInt()
{
Scanner sc = new Scanner(System.in);
int i = sc.nextInt();
return i;
}
// more methods here
}
Sending objects as parameters….
public class ParameterTest
{
public static void main(String[ ] args)
{
BankAccount acc = new BankAccount("1", "Samsun Okoyo");
test(acc);
System.out.println("Account Number: " + acc.getAccountNumber());
System.out.println("Account Name: " + acc.getAccountName());
System.out.println("Balance: " + acc.getBalance());
}
private static void test(BankAccount accIn)
{
accIn.deposit(2500);
}
}
Account Number: 1
Account Name: Samsun Okoyo
Balance: 2500.0
Effect on computer memory of sending an object as a parameter…
public static void main (String[] args)
{
BankAccount acc = new BankAccount(…) ;
}
Computer Memory Java Instructions
acc
a BankAccount
object
private static void test(BankAccount accIn)
{
}
accIn
test(acc);
accIn.deposit(2500);
Practical Work
StudentstudentNumber : StringstudentName : StringmarkForMaths : intmarkForEnglish : intmarkForScience : int
Student(String, String)getNumber() : String getName() : String enterMarks(int, int, int) getMathsMark() : intgetEnglishMark() : int getScienceMark() : int calculateAverageMark() : double
public class Student
{
// attributes
// methods
}
Implement this class in your practical
StudentstudentNumber : StringstudentName : StringmarkForMaths : intmarkForEnglish : intmarkForScience : int
Student(String, String)getNumber() : String getName() : String enterMarks(int, int, int) getMathsMark() : intgetEnglishMark() : int getScienceMark() : int calculateAverageMark() : double
public class Student
{
// attributes
// methods
}
Implement this class in your practical
StudentstudentNumber : StringstudentName : StringmarkForMaths : intmarkForEnglish : intmarkForScience : int
Student(String, String)getNumber() : String getName() : String enterMarks(int, int, int) getMathsMark() : intgetEnglishMark() : int getScienceMark() : int calculateAverageMark() : double
public class Student
{
private int markForMaths;
// more attributes here
// methods
}
Implement this class in your practical
StudentstudentNumber : StringstudentName : StringmarkForMaths : intmarkForEnglish : intmarkForScience : int
Student(String, String)getNumber() : String getName() : String enterMarks(int, int, int) getMathsMark() : intgetEnglishMark() : int getScienceMark() : int calculateAverageMark() : double
public class Student
{
private int markForMaths;
// more attributes here
// methods
}
Implement this class in your practical
StudentstudentNumber : StringstudentName : StringmarkForMaths : intmarkForEnglish : intmarkForScience : int
Student(String, String)getNumber() : String getName() : String enterMarks(int, int, int) getMathsMark() : intgetEnglishMark() : int getScienceMark() : int calculateAverageMark() : double
Implement this class in your practical
public class Student
{
private int markForMaths;
// more attributes here
public int getMathsMark( ) {
return markForMaths; }
// more methods here
}
StudentstudentNumber : StringstudentName : StringmarkForMaths : intmarkForEnglish : intmarkForScience : int
Student(String, String)getNumber() : String getName() : String enterMarks(int, int, int) getMathsMark() : intgetEnglishMark() : int getScienceMark() : int calculateAverageMark() : double
Then write a tester to check your class
StudentstudentNumber : StringstudentName : StringmarkForMaths : intmarkForEnglish : intmarkForScience : int
Student(String, String)getNumber() : String getName() : String enterMarks(int, int, int) getMathsMark() : intgetEnglishMark() : int getScienceMark() : int calculateAverageMark() : double
Then write a tester to check your class
public class StudentTester
{
public static void main(String[ ] args) {
}
}
StudentstudentNumber : StringstudentName : StringmarkForMaths : intmarkForEnglish : intmarkForScience : int
Student(String, String)getNumber() : String getName() : String enterMarks(int, int, int) getMathsMark() : intgetEnglishMark() : int getScienceMark() : int calculateAverageMark() : double
Then write a tester to check your class
public class StudentTester
{
public static void main(String[ ] args) {
/* code to create at least two Student objects and call
their methods */ }
}
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