Two Design Patterns: Adapter and Composite

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Two Design PatternsAdapter and Composite

• C Sc 335

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Adapter

• The intent of Adapter is to provide the interface
  a client expects, using the services of a class
  with a different interface
• We have used Adapter (also known as Wrapper)
• Adapted HashMap to Jukebox to allow a small set
  of methods particular to the Jukebox
• Adapted ArrayList to store Songs and CDs
• Sometime the Adapter extends a class or
  implements an interface used in the client code

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Object Adapter

• JTable needs an instance of TableModel that
  represents data
• It must have methods like
• getColumnCount, getRowCount, getValueAt
• You can adapt any of your data to the interface
  expected by JTable by implementing all methods

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Show Table of Employees

• public static void main(String args)
• WeeklyEmployee w1
• new WeeklyEmployee("Devon", 40.0, 15.75, 3,
  "M")
• WeeklyEmployee w2
• new WeeklyEmployee("Kim", 0.0, 12.50, 1,
  "S")
• WeeklyEmployee w3
• new WeeklyEmployee("Chris", 35.0, 20.50, 2,
  "M")
• WeeklyEmployee employees w1, w2, w3
• EmployeeTable empTable
• new EmployeeTable(employees)
• EmployeeTableFrame window
• new EmployeeTableFrame(empTable)
• window.show()

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The View

• class EmployeeTableFrame extends JFrame
• private JTable view
• public EmployeeTableFrame(EmployeeTable
  empTable)
• setTitle("Adapter")
• setSize(300, 200)
• view new JTable(empTable)
• getContentPane().add(view)
• pack()

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EmployeeTable class

• class EmployeeTable implements TableModel
• private int rows, cols
• private WeeklyEmployee data
• public EmployeeTable(WeeklyEmployee
  employeeData)
• data employeeData
• cols 4
• rows data.length

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Team Activity

• public int getColumnCount()
• // What goes here?
• public int getRowCount()
• // What goes here?

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JTable Populates Cells

• public Object getValueAt(int row, int col)
• if (col 0)
• return datarow.getName()
• else if (col 1)
• return "" datarow.grossPay()
• else if (col 2)
• return "" datarow.getTotalTaxes()
• else if (col 3)
• return "" (datarow.grossPay() -
• datarow.getTotalTaxes())
• else return null

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Needs formatting
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Extend or Implement?

• Still need 7 more methods if implementing
  TableModel, in which case, you need
• public Class getColumnClass(int col)
• return getValueAt(0, col).getClass()
• Or could extend AbstractTableModel
• then override the methods

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Composite Design Pattern

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

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General Form
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Client

• Portfolio overall new Portfolio("my IRA")
• // Add one leaf
• overall.add(new Stock("Seven Eleven", 500,
  9.15))
• // Build and add a Portfolio to a Portfolio
• Portfolio tech new Portfolio("Tech stocks")
• Stock s1 new Stock("Sun", 20, 30.50)
• tech.add(s1)
• tech.add(new MutualFund("Microsoft", 13, 45.20))
• overall.add(tech)
• // Can update prices
• s1.updatePrice(31.50) // up 50 cents
• // Show all elements with indents
• overall.listAll()

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Desired Output

• my IRA 5762.6
• 500 shares Seven Eleven 4575.0
• Tech stocks 1187.6
• 20 shares Sun 600.0
• 13.0 shares Microsoft 587.6

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Team Activity

• A) Draw the UML Diagram to capture the real
  world example of stocks, mutual funds, and
  portfolios
• List all class names
• Draw the relationships
• Place the listAll method in the correct place
• Place the add method in the correct place
• Place the getValue methods in the correct place

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An 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
• B) Using the UML diagram, write the Java code for
  Asset and Commodity (a leaf)

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Answer

• 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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Answer

• 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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Stock and MutualFund

• C) Implement Mutual Fund and Stock
• D) Implement Portfolio with the getValue method
  only (no listAll)

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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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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