Adapter Design Pattern

1
Adapter Design Pattern

• C Sc 335
• Rick Mercer

2
Adapter

• The intent of Adapter is to provide the interface
  a client expects, using a class with a different
  interface (methods)
• Sometimes called a wrapper because an adapter
  class wraps the implementation of another class
  in the desired interface

3
In Java 1.4

• Before Java 5.0, we often adapted an ArrayList or
  HashMap to have an easier to use collection see
  wiki
• Use a Containment Relationship
• A collection class with an ArrayList or HashMap
  instance variable
• Put the cast in the method once instead of
  throughout code
• http//www.refactoring.com/catalog/encapsulateDown
  cast.html
• Add Employees rather than Objects (type safe)
• Method names mean more to the client
• getEmployeeWithID rather than get
• Not as compelling for use with Java 5
• Generics now provides type safety
• No need to cast

4
Object Adapter

• Adapters also come about by extending a class or
  implementing an interface used by the client code
• You have used Adapter in this manner
• Adapted your song collection so it could be
  stored in a ListModel object, which in turn was
  used by a JList to show a graphical view of the
  list elements

5
JTable is like JList

• In a similar fashion, JTable needs an instance of
  TableModel that represents the model (data)
• JTable Graphical view of data, rows/columns
• Your new class must have methods such as
• getColumnCount, getRowCount, getValueAt
• Why? Because JTable uses them to populate view
• You adapt your data to the interface expected by
  JTable by implementing all 10 methods

6
EmployeeTable class

• // Store an array of Employee objects that
• // can be put into a table
• import javax.swing.event.TableModelListener
• import javax.swing.table.TableModel
• public class EmployeeList implements TableModel
• private int rows 3
• private int cols 4
• private Employee data new Employeerows
• public EmployeeList()
• data0 new Employee("Devon",40, 15.75, 3,
  "M")
• data1 new Employee("Kim", 0, 12.50, 1,
  "S")
• data2 new Employee("Chris", 35, 20.50,
  2,"M")
• // continued

7
JTable Populates Cells

• // Part of the TableModel interface
• public Object getValueAt(int row, int col)
• switch (col)
• case 0
• return datarow.getName()
• case 1
• return datarow.grossPay()
• case 2
• return datarow.incomeTax()
• case 3
• return datarow.grossPay()-datarow.incomeTa
  x()
• default
• return null

8
Implement 2 More Methods

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

9
The View

• class EmployeeFrame extends JFrame
• public static void main(String args)
• new EmployeeFrame().setVisible(true)
• public EmployeeFrame()
• EmployeeList threeEmps new EmployeeList()
• setTitle("Adapter")
• setSize(300, 120)
• setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE)
  
• JTable view new JTable(threeEmps)
• JScrollPane scroller new JScrollPane(view)
• this.add(scroller, BorderLayout.CENTER)

10
A JModel in a JTable

• This could also be done by extending class
  AbstractTableMode
• See MouseAdapter and WindowAdapter

11
JTree and TreeModel

• An adapter could also convert the interface of a
  Document Object Model of an XML document into a
  tree structure that can be displayed

lt?xml version'1.0' encoding'utf-8'?gt ltslideshow
title"Sample Slide Show" date"Date of
publication" author"Yours Truly"gt ltslide
type"all"gt lttitlegtWake up to
WonderWidgets!lt/titlegt lt/slidegt ltslide
type"all"gt lttitlegtOverviewlt/titlegt
ltitemgtWhy ltemgtWonderWidgetslt/emgt are
greatlt/itemgt ltitem/gt ltitemgtWho
ltemgtbuyslt/emgt WonderWidgetslt/itemgt
lt/slidegt lt/slideshowgt
12
MouseAdapter

• Swing include Adapters to provide an object with
  all the methods needed to implement an interface
• Demo MouseAdapter
• A class that implements all methods expected by a
  MouseListener and MouseMotionListener
• Convenience? You override what few methods you
  need
• WindowAdapter ...