Implementing Classes Learning objectives By the end of this lecture you should be able to: • design classes using the notation of the Unified Modeling 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; • implement collection classes based on arrays.
Implementing Classes Learning objectives By the end of this lecture you should be able to: design classes using the notation of the Unified Modeling Language.
Dec 16, 2015
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Implementing Classes
Learning objectives
By the end of this lecture you should be able to:
• design classes using the notation of the Unified Modeling 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;
• implement collection classes based on arrays.
Implementing classes in Java
A class consists of:
a set of attributes (the data);
a set of methods
Oblong
length
height : double
: double
setLength
setHeight
getLength
getHeight
calculateArea
calculatePerimeter
Oblong
()
: double
(double)
(double)
()
()
()
: double
: double
: double
(double, double)
The notation of the Unified Modeling Language (UML)
Oblong
length : double
height : double
Oblong(double, double)
setLength(double)
setHeight(double)
getLength() : double
getHeight() : double
calculateArea() : double
calculatePerimeter() : double
public class Oblong
{
double length;
double height;
private
private
public Oblong(double lengthIn, double heightIn)
{
}
// more methods here
}
length = lengthIn;
height = heightIn;
getLength()
{
}
public double
return length;
getHeight()
{
}
public double
return height;
setLength( )
{
}
public void
length = lengthIn;
double lengthIn
setHeight( )
{
}
public void
height = heightIn;
double heightIn
calculateArea()
{
}
public double
return length * height;
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 BankAccount(String numberIn, String nameIn)
{
accountNumber = numberIn;
accountName = nameIn;
balance = 0;
}
public String getAccountName()
{
return accountName;
}
public String getAccountNumber()
{
return accountNumber;
}
public double getBalance()
{
return balance;
}
public void deposit(double amountIn)
{
balance = balance + amountIn;
}
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 ();
acc2.getInterestRate();
acc3.deposit( 500 );
acc3.setInterestRate(1.5);
Bank.setInterestRate(1.4);
Bank.getInterestRate();
The static keyword
private static double interestRate;
public static void setInterestRate(double rateIn)
{
interestRate = rateIn;
}
public static double getInterestRate()
{
return interestRate;
}
The addInterest method
public void addInterest()
{
balance = balance + (balance * interestRate)/100;
}
public class BankAccountTester2
{
public static void main(String[] args)
{
BankAccount2 account1 =
new BankAccount2("99786754","Varinder Singh");
BankAccount2 account2 =
new BankAccount2("99887776","Lenny Roberts");
account1.deposit(1000);
account2.deposit(2000);
BankAccount2.setInterestRate(10);
account1.addInterest();
System.out.println("Account number: " + account1.getAccountNumber());
System.out.println("Account name: " + account1.getAccountName());
System.out.println("Interest Rate " + BankAccount2.getInterestRate());
System.out.println("Current balance: " + account1.getBalance());
System.out.println();
System.out.println("Account number: " + account2.getAccountNumber());
System.out.println("Account name: " + account2.getAccountName());
System.out.println("Interest Rate " + BankAccount2.getInterestRate());
System.out.println("Current balance: " + account2.getBalance());
}
}
Account number: 99786754
Account name: Varinder Singh
Interest rate: 10.0
Current balance: 1100.0
Account number: 99887776
Account name: Lenny Roberts
Interest rate: 10.0
Current balance: 2000.0
Initializing attributes
Java does not give an initial value to local variables but does initialize attributes;
int
double
char
Objects0
boolean false null
private static double interestRate = 0;
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
}
public static double nextDouble()
{
Scanner sc = new Scanner(System.in);
double d = sc.nextDouble();
return d;
}
public static String nextString()
{
Scanner sc = new Scanner(System.in);
String s = sc.nextLine();
return s;
}
public static char nextChar()
{
Scanner sc = new Scanner(System.in);
char c = sc.next().charAt(0);
return c;
}
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
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);
Collection classes
When one object itself consists of other objects, this relationship is called aggregation;
A collection class is an implementation of the aggregation relationship.
BankAccountBank *
Bank
list: BankAccount [ ]
total : int
Bank(int)
search(String) : int
getTotal() : int
isEmpty() : boolean
isFull() : boolean
add(BankAccount) : boolean
getItem(String) : BankAccount
depositMoney(String, double) : boolean
withdrawMoney(String, double) : boolean
remove(String) : boolean
public class Bank
{
private BankAccount[] list;
private int total;
public Bank(int sizeIn)
{
list = new BankAccount[sizeIn];
total = 0;
}
private int search(String accountNumberIn)
{
for(int i = 0; i ; i++)
{
}
return -999;
}
BankAccount tempAccount = list[i];
String tempNumber
= tempAccount.getAccountNumber();
if(tempNumber.equals(accountNumberIn))
{
return i;
}
< total
public int getTotal(){ return total;}
public boolean isEmpty(){ if (total == 0) { return true; } else { return false; }}
public boolean isFull()
{
if (total == list.length)
{
return true;
}
else
{
return false;
}
}
public boolean add(BankAccount accountIn)
{
if( )
{
return true;
}
else
{
return false;
}
}
(!isFull()
list[total] = accountIn;
total++;
public BankAccount getItem(String accountNumberIn)
{
int index;
index = search(accountNumberIn);
if(index == -999)
{
return null;
}
else
{
return list[index];
}
}
public boolean depositMoney
(String accountNumberIn, double amountIn)
{
int index = search(accountNumberIn);
if(index == -999)
{
return false;
}
else
{
list[index].deposit(amountIn);
return true;
}
}
public boolean remove(String numberIn)
{
int index = search(numberIn);
if(index == -999)
{
return false;
}
else
{
// remove item from list
return true;
}
}
4th item
3rd item
2nd item
1st item
Item to delete
5th item Smith
Adams
Patel
Okoya
Ling
Patel
Adams
Smith
list
list[index] = list[index+1];
list[index+1] = list[index+2];
list[index+2] = list[index+3];
total--;
list[i] = list[i+1];
for(int i = index; i<= total-2; i++)
{
}
public class BankProgram
{
public static void main(String[] args)
{
char choice;
int size;
System.out.print("Maximum number of accounts? ");
size = EasyScanner.nextInt();
Bank myBank = new Bank(size);
do
{
System.out.println();
System.out.println("1. Create new account");
System.out.println("2. Remove an account");
System.out.println("3. Deposit money");
System.out.println("4. Withdraw money");
System.out.println("5. Check account details");
System.out.println("6. Quit");
System.out.println();
System.out.print("Enter choice [1-6]: ");
choice = EasyScanner.nextChar();
System.out.println();
switch (choice)
{
case '1': option1(myBank); break;
case '2': option2(myBank); break;
case '3': option3(myBank); break;
case '4': option4(myBank); break;
case '5': option5(myBank); break;
case '6': break;
default: System.out.println("Invalid entry");
}
}while (choice != '6');
}
// add account
private static void option1(Bank bankIn)
{
System.out.print("Enter account number: ");
String number = EasyScanner.nextString();
System.out.print("Enter account name: ");
BankAccount account = new BankAccount(number, name);
boolean ok = bankIn.add(account);
if (!ok)
{
System.out.println("The list is full");
}
else
{
System.out.println("Account created");
}
}
// remove account
private static void option2(Bank bankIn)
{
System.out.print("Enter account number: ");
String number = EasyScanner.nextString();
boolean ok = bankIn.remove(number);
if (!ok)
{
System.out.println("No such account number");
}
else
{
System.out.println("Account removed");
}
}
// deposit money
private static void option3(Bank bankIn)
{
System.out.print("Enter account number: ");
String number = EasyScanner.nextString();
System.out.print("Enter amount to deposit: ");
double amount = EasyScanner.nextDouble();
boolean ok = bankIn.depositMoney(number, amount);
if (!ok)
{
System.out.println("No such account number");
}
else
{
System.out.println("Money deposited");
}
}
// withdraw money from an account
private static void option4(Bank bankIn)
{
System.out.print("Enter account number: ");
String number = EasyScanner.nextString();
System.out.print("Enter amount to withdraw: ");
double amount = EasyScanner.nextDouble();
boolean ok = bankIn.withdrawMoney(number, amount);
if (!ok)
{
System.out.println("No such account number");
}
else
{
System.out.println("Money withdrawn");
}
}
// check account detailsprivate static void option5(Bank bankIn){ System.out.print("Enter account number "); String number = EasyScanner.nextString(); BankAccount account = bankIn.getItem(number); if (account == null) { System.out.println("No such account number"); } else { System.out.println("Account number: " +
account.getAccountNumber()); System.out.println("Account name: " +
account.getAccountName()); System.out.println("Balance: " +
account.getBalance()); System.out.println(); }}
Maximum number of accounts? 100
1. Create new account
2. Remove an account
3. Deposit money
4. Withdraw money
5. Check account details
6. Quit
Enter choice [1-6]: 1
1. Create new account
2. Remove an account
3. Deposit money
4. Withdraw money
5. Check account details
6. Quit
Enter choice [1-6]:
Enter account number:
Enter account name:
Account created
63488965
Paula Wilkins
1
1. Create new account
2. Remove an account
3. Deposit money
4. Withdraw money
5. Check account details
6. Quit
Enter choice [1-6]:
Enter account number:
Enter account name:
Account created
14322508
Sydney Isaacs
1
1. Create new account
2. Remove an account
3. Deposit money
4. Withdraw money
5. Check account details
6. Quit
Enter choice [1-6]:
Enter account number:
Enter account name:
Account created
90871435
Delroy Joseph
3
1. Create new account
2. Remove an account
3. Deposit money
4. Withdraw money
5. Check account details
6. Quit
Enter choice [1-6]:
Enter account number:
Enter amount to deposit:
Money deposited
90871435
1500
2
1. Create new account
2. Remove an account
3. Deposit money
4. Withdraw money
5. Check account details
6. Quit
Enter choice [1-6]:
Enter account number:
Account removed
14322508
5
1. Create new account
2. Remove an account
3. Deposit money
4. Withdraw money
5. Check account details
6. Quit
Enter choice [1-6]:
Enter account number:
No such account number
14322508
5
1. Create new account
2. Remove an account
3. Deposit money
4. Withdraw money
5. Check account details
6. Quit
Enter choice [1-6]:
Enter account number:
Account number: 90871435
Account name: Delroy Joseph
Balance: 1500.0
90871435
6
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