Composite Design Pattern

1
Composite Design Pattern

• Rick Mercer
• C Sc 335

2
Composite Design Pattern

• Compose objects into tree structures to represent
  part-whole hierarchies.
• Composite lets clients treat individual objects
  and compositions of objects uniformly

3
General Form
4
Client

• Portfolio overall new Portfolio("my IRA")
• // Add two leafs to "my IRA"
• overall.add(new Stock("Seven Eleven", 500,
  9.15))
• overall.add(new BankAccount("Swiss Account",
  300000))
• // Create a tech portfolio
• Portfolio tech new Portfolio("Tech stocks")
• Stock sun new Stock("Sun", 20, 30.50)
• MutualFund highRisk
• new MutualFund("Nasdaq", 13, 45.20)
• tech.add(sun) // add leaf
• tech.add(highRisk) // add leaf
• // Add this 2nd portfolio to the overall
  portfolio
• overall.add(tech) // add Composite
• // Show all elements with indents (output next
  slide
• overall.listAll()

5
Desired Output

• my IRA 305772.6
• 500 shares Seven Eleven 4575.0
• Swiss Account 300000.0
• Tech stocks 1197.6
• 20 shares Sun 610.0
• 13.0 shares Nasdaq 587.6

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Team Activity

• A) Let a UML Diagram capture the real world
  example of bank accounts stocks, mutual funds,
  and portfolios
• List base class as Asset (Component from slide 3)
• Let Commodity extend Asset (there are 2 commodity
  types)
• Stock extends Commodity (a leaf)
• MutualFund extends Commodity (a leaf)
• Let BankAccount extend Asset (a leaf)
• Let Portfolio extend Asset (Composite from slide
  3)
• Can store Stocks, BankAccounts, MutualFunds
  (leafs) or other Portfolios (Composite) because
  they are all assets
• Place these methods in the correct place
• listAll add getValue

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One Answer
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Implement Asset Commodity

• While the Value of a Portfolio is the sum of all
  assets, the value of a Commodity is the shares
  times the price
• Using the UML diagram, write tests and Java code
  for
• Asset
• BankAccount
• Commodity
• Stock
• MutualFund

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Asset

• abstract class Asset
• private String myName
• public Asset(String name)
• myName name
• public String toString()
• return myName " " getValue()
• public abstract double getValue()

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BankAccount

• class BankAccount extends Asset
• private double balance
• public BankAccount(String name, double
  initialBalance)
• super(name)
• balance initialBalance
• public double getValue()
• return balance

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Commodity

• abstract class Commodity extends Asset
• private double myUnits
• private double myPrice
• public Commodity(String name, double shares,
  double price)
• super(name)
• myUnits shares
• myPrice price
• public double getValue()
• return myUnits myPrice

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Answer

• class Stock extends Commodity
• public Stock(String company, int shares, double
  price)
• super(shares " shares " company, price,
  shares)
• class MutualFund extends Commodity
• public MutualFund(String fund, double shrs,
  double price)
• super(shares " shares " fund, shrs,
  price)

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Stock and MutualFund

• D) Implement Portfolio with the getValue method
  only (no listAll)

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Answer

• class Portfolio extends Asset
• private ArrayList myAssets
• public static final String INDENT " "
• public Portfolio(String name)
• super(name)
• myAssets new ArrayList()
• public void add(Asset h)
• myAssets.add(h)
• public double getValue()
• double sum 0.0
• Iterator itr myAssets.iterator()
• while (itr.hasNext())
• sum ((Asset) itr.next()).getValue()
• return sum