CSC 335 ObjectOriented Programming and Design

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CSC 335 Object-Oriented Programming and Design

• Week 3
• ATM and other Things

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Outline for Tuesday, 10-Aug

• Happenings see happenings page or these slides
• There are several important announcements
• ATM System
• The Big Picture
• Design
• The little details that have caused confusion
• Things we should all know now
• show such topics from presentation 2 quickly

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Happenings

• Quiz every Thursday
• Quiz 1 will be 12-Sep
• Show output from a class, write a class
• Section will be held
• In your assigned room, not Gould Simpson
• 1) 0800AM-0850AM M BIO E 307
• 2) 0900AM-0950AM M BIO E 307
• 3H) 1100AM-1150AM M PAS 416
• 4) 1200PM-1250PM M BIO E 307
• 5) 0100PM-0150PM M BIO E 307
• 6) 0200PM-0250PM M HAURY 219
• 8) 0400PM-0450PM M HARV 303
• 9) 0500PM-0550PM M HARV 303 (may be
  cancelled)

4
Happenings continued

• Projects Due Tomorrow _at_ 1000 p.m.
• ATM Phase 1
• The Model so all 4 unit test pass (4 working
  classes)
• Lab1
• The assignment from Monday Section
• See the end of the exercise for turn in
  instructions

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Happenings continued

• Review Session Tonight!
• Optional Java Review session
• 700 to ??? 10-September
• Gould Simpson 701
• GS may be locked, enter with card by 228GS
• Section Leaders will review Java, answer
  questions, and may offer additional lab hours in
  228GS after the review session

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Object come from Classespreviously shown in
presentation 2

• Classes model real world entities that are more
  complex than numbers ints, doubles
• Each class has a collection of related methods
  and data that the methods need to fulfill their
  responsibility.
• A class is the blueprint for constructing any
  number of objects
• A system can be modeled as collection of classes
  
• On the next slide, identify the things that model
  real world entities or classes

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Find real world entities (classes) previously
shown

• Implement the software for an automated bank
  teller machine so it allows many bank customers
  to access bank accounts through a unique
  identification. The customer, may complete any of
  the following transactions withdraw money,
  deposit money, query account balances, and see
  the most recent ten (10) transactions. The system
  must maintain the correct balances for all
  accounts. The system must be able to process one
  or more transactions for any number of customers.

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Nouns are possible classes previously shown

• Potential classes to model a solution
• Bank Teller
• Identification Number
• Customer
• Transaction
• Most recent 10 transactions
• BankAccount
• Window
• What are the responsibilities of a bank account?
• What should each instance be able to do?
• What should each instance know?

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A BankAccount classpreviously shown

• BankAccount models one account at a bank
• This class could have this collection of methods
  what each instance can do
• withdraw
• deposit
• getBalance // return account balance
• getID // return account name
• and these instance variables what each instance
  knows
• String ID
• double balance

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Instance variablespreviously shown

• Each BankAccount object has its own state
• Java stores state in instance variables
• each instance of BankAccount (each object) has
  two values to store the values a String and a
  number
• each instance of a class (object) maintains its
  own set of values in the instance variables.
• If there are 6397 BankAccount objects, there are
  6397 Ids and 6397 balances
• Classes have methods that do things or return
  information (summary of methods shown next)

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This is not a BankAccountpreviously shown

• Relationship between a class and the instances
• Each object has its own instance variables

UML comments
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Other classes for ATMnew

• Other classes include
• BankAccountCollection Maintains a collection of
  all BankAccounts
• Suggested data structure HashMap see Java API
• fast lookup based on a key (account id), order
  not important
• Transaction Maintain a record of each withdrawal
  and deposit
• TransactionLog Maintain list of all Transactions
• Suggested Data Structure ArrayList see Java API
• The ordering counts (get 10 most recent)

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Design

• Design means many things
• Currently, design means
• Deciding which classes to have (and their names)
• Responsibilities to build the model for ATM
• These have been assigned to 4 classes
• Naming methods, determining return types, and the
  parameters each method needs
• Deciding how to record a Transaction
• The could have been other method signatures
• public Transaction(String AccountID,
• String currentBalance,
• double amount,
• int transactionType)

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Design

• Design is about making decisions
• The relationship between BankAccount and
  Transaction could be quite different
• Rick made a decision to do it one way
• you may have a different design
• Transaction makes the deposit or withdrawal
• BankAccount returns a Transaction
• Have DepositTransaction and WithdrawTransaction
• Could have had a Customer with a list of accounts
• With ATM Phase 1 to learn unit testing, you are
  stuck with Rick's design decisions
• You will make many design decisions in other
  projects

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View the Design

• There are several views of the design
• The unit tests you have
• Has method signatures and behavior as booleans
• A main method that shows how the objects can work
  together
• On upcoming slides
• A JBuilder UML view (need enterprise edition to
  see it, so I've added a picture)
• On an upcoming slide

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• package atm // RunBankTeller.java
• // Show all four classes working together. This
  "big" picture
• // view is meant to demonstrate the behavior of
  the four
• // classes you are currently building. The main
  method is
• // like a mediator in that it coordinates
  activities between
• // different types of objects that do not know
  each other.
• public class RunBankTeller
• public static final int MAX_TRANSACTIONS 10
• public static void main(String args)
• // Initialize both collections
• BankAccountCollection allAccounts
• new
  BankAccountCollection()
• allAccounts.add( new BankAccount("A", 111.11,
  "1111"))
• allAccounts.add( new BankAccount("B", 222.22,
  "2222"))
• allAccounts.add( new BankAccount("C", 333.33,
  "3333"))
• allAccounts.add( new BankAccount("D", 444.44,
  "4444"))

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• // No transactions for the account with ID "A"
• // Imagine "A" came from the user interface
• String XPress10 log.getMostRecent("A",
  MAX_TRANSACTIONS)
• System.out.println(XPress10)
• // Hard code 2 transactions (with a 10 ms delay
  between them)
• BankAccount currentAccount
• allAccounts.findAccountWithI
  D("A")
• // Imagine "123.45" came from the user interface
• double currentAmount 123.45
• currentAccount.deposit(currentAmount)
• Transaction t new Transaction(currentAccount,
• currentAmount,
• 
  Transaction.DEPOSIT_CODE)
• System.out.println()
• System.out.println("Deposit transaction " t)
• log.addTransaction(t)
• // Output so far

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• // cause a 0.01 second delay
• try
• Thread.currentThread().sleep(10)
• catch(Exception e)
• // Imagine "98.76" came from the user interface
• currentAmount 98.76
• currentAccount.withdraw(currentAmount)
• t new Transaction(currentAccount,
  currentAmount, Transaction.WITHDRAW_CODE)
• System.out.println()
• System.out.println("Withdraw transaction " t)
• log.addTransaction(t)
• // Now "A" should have two transactions
• XPress10 log.getMostRecent("A", 10)
• System.out.println()
• System.out.println(XPress10)
• // output from the code above

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JBuilder UML Diagram link
Package A collection of classes and interfaces.
This small program uses classes from 4 packages.
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ATM Details

• We had 2 Questions about Transaction
• Why does the Transaction constructor need
  BankAccount?
• To get the ID and the current balance and store
  this data
• What do hasCleared and setCleared mean?
• At some point the transaction would become part
  of your ledger balance (not just available
  balance)
• We will not actually use these methods in ATM,
  sorry.
• However, you must implement both methods
• They manage a boolean flag, there is not fancy
  algorithm
• Any other questions with ATM Phase 1?

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Finish Presentation 2

• Last Thursday's presentation listed several
  topics that may not be known by everyone
• We will go through them quickly
• Slides 2-23 through 2-4657
• Can learn more from
• review session tonight
• from Java in 21 Days
• from your 127A/B or 227 book
• from some other Java book
• Recommended
• Take always take JavaIn21Days to lab as a
  reference
• read or skim chapters 1-4 of JavaIn21Days