SE450: Horstmann Chapter 5

LinkedList<String> list = . . .;
ListIterator<String> iterator = list.listIterator();
while (iterator.hasNext())
{
   String current = iterator.next();
   . . .
}

Why iterators?

Classical List Data Structure [4/72]

Traverse links directly

Link currentLink = list.head;
while (currentLink != null)
{
   Object current = currentLink.data;
   currentLink = currentLink.next;
}

Exposes implementation
Error-prone

High-Level View of Data Structures [5/72]

Queue
Array with random access
List
???

List with Cursor [6/72]

for (list.reset(); list.hasNext(); list.next())
{
   Object x = list.get();
   . . .
}

Disadvantage: Only one cursor per list
Iterator is superior concept

The Pattern Concept [7/72]

History: Architectural Patterns
Christopher Alexander
Each pattern has
- a short name
- a brief description of the context
- a lengthy description of the problem
- a prescription for the solution

Short Passages Pattern [8/72]

Short Passages Pattern [9/72]

Context

"...Long, sterile corridors set the scene for everything bad about modern architecture..."

Problem

a lengthy description of the problem, including

a depressing picture
issues of light and furniture
research about patient anxiety in hospitals
research that suggests that corridors over 50 ft are considered uncomfortable

Short Passages Pattern [10/72]

Solution

Keep passages short. Make them as much like rooms as possible, with carpets or wood on the floor, furniture, bookshelves, beautiful windows. Make them generous in shape and always give them plenty of light; the best corridors and passages of all are those which have windows along an entire wall.

Iterator Pattern [11/72]

Context

An aggregate object contains element objects
Clients need access to the element objects
The aggregate object should not expose its internal structure
Multiple clients may want independent access

Iterator Pattern [12/72]

Solution

Define an iterator that fetches one element at a time
Each iterator object keeps track of the position of the next element
If there are several aggregate/iterator variations, it is best if the aggregate and iterator classes realize common interface types.

Iterator Pattern [13/72]

Iterator Pattern [14/72]

Names in pattern are examples
Names differ in each occurrence of pattern

Name in Design Pattern	Actual Name (linked lists)
Aggregate	List
ConcreteAggregate	LinkedList
Iterator	ListIterator
ConcreteIterator	anonymous class implementing `ListIterator`
createIterator()	listIterator()
next()	next()
`isDone()`	opposite of `hasNext()`
`currentItem()`	return value of `hasNext()`

Model/View/Controller [15/72]

Some programs have multiple editable views
Example: HTML Editor
- WYSIWYG view
- structure view
- source view
Editing one view updates the other
Updates seem instantaneous

Model/View/Controller [16/72]

Model/View/Controller [17/72]

Model: data structure, no visual representation
Views: visual representations
Controllers: user interaction

Model/View/Controller [18/72]

Views/controllers update model
Model tells views that data has changed
Views redraw themselves

Model/View/Controller [19/72]

Observer Pattern [20/72]

Model notifies views when something interesting happens
Button notifies action listeners when something interesting happens
Views attach themselves to model in order to be notified
Action listeners attach themselves to button in order to be notified
Generalize: Observers attach themselves to subject

Observer Pattern [21/72]

Context

An object, called the subject, is source of events
One or more observer objects want to be notified when such an event occurs.

Solution

Define an observer interface type. All concrete observers implement it.
The subject maintains a collection of observers.
The subject supplies methods for attaching and detaching observers.
Whenever an event occurs, the subject notifies all observers.

Observer Pattern [22/72]

Names in Observer Pattern [23/72]

Name in Design Pattern	Actual Name (Swing buttons)
Subject	`JButton`
Observer	`ActionListener`
ConcreteObserver	the class that implements the `ActionListener` interface type
attach()	`addActionListener()`
notify()	`actionPerformed()`

Layout Managers [24/72]

User interfaces made up of components
Components placed in containers
Container needs to arrange components
Swing doesn't use hard-coded pixel coordinates
Advantages:
- Can switch "look and feel"
- Can internationalize strings
Layout manager controls arrangement

Layout Managers [25/72]

FlowLayout: left to right, start new row when full
BoxLayout: left to right or top to bottom
BorderLayout: 5 areas, Center, North, South, East, West
GridLayout: grid, all components have same size
GridBagLayout: complex, like HTML table

Layout Managers [26/72]

Layout Managers [27/72]

Set layout manager
JPanel keyPanel = new JPanel(); keyPanel.setLayout(new GridLayout(4, 3));
Add components
for (int i = 0; i < 12; i++) keyPanel.add(button[i]);

Layout Managers [28/72]

Voice Mail System GUI [29/72]

Same backend as text-based system
Only Telephone class changes
Buttons for keypad
Text areas for microphone, speaker

Voice Mail System GUI [30/72]

Voice Mail System GUI [31/72]

Arrange keys in panel with GridLayout:

JPanel keyPanel = new JPanel(); 
keyPanel.setLayout(new GridLayout(4, 3)); 
for (int i = 0; i < 12; i++) 
{ 
   JButton keyButton = new JButton(...); 
   keyPanel.add(keyButton); 
   keyButton.addActionListener(...);
}

Voice Mail System GUI [32/72]

Panel with BorderLayout for speaker

JPanel speakerPanel = new JPanel(); 
speakerPanel.setLayout(new BorderLayout()); 
speakerPanel.add(new JLabel("Speaker:"), BorderLayout.NORTH); 
speakerField = new JTextArea(10, 25); 
speakerPanel.add(speakerField, BorderLayout.CENTER);

Voice Mail System GUI [33/72]

Add speaker, keypads, and microphone panel to frame
Frame already has BorderLayout

file:horstmann/ch05_mailgui/Telephone.java [source] [doc-public] [doc-private]

package horstmann.ch05_mailgui;
import java.awt.BorderLayout;
import java.awt.GridLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextArea;

/**
   Presents a phone GUI for the voice mail system.
 */
public class Telephone
{
  /**
      Constructs a telephone with a speaker, keypad,
      and microphone.
   */
  public Telephone()
  {
    JPanel speakerPanel = new JPanel();
    speakerPanel.setLayout(new BorderLayout());
    speakerPanel.add(new JLabel("Speaker:"),
        BorderLayout.NORTH);
    speakerField = new JTextArea(10, 25);
    speakerPanel.add(speakerField,
        BorderLayout.CENTER);

    String keyLabels = "123456789*0#";
    JPanel keyPanel = new JPanel();
    keyPanel.setLayout(new GridLayout(4, 3));
    for (int i = 0; i < keyLabels.length(); i++)
    {
      final String label = keyLabels.substring(i, i + 1);
      JButton keyButton = new JButton(label);
      keyPanel.add(keyButton);
      keyButton.addActionListener(event -> connect.dial(label));
    }

    final JTextArea microphoneField = new JTextArea(10,25);

    JButton speechButton = new JButton("Send speech");
    speechButton.addActionListener(event -> {
      connect.record(microphoneField.getText());
      microphoneField.setText("");
    });

    JButton hangupButton = new JButton("Hangup");
    hangupButton.addActionListener(event -> connect.hangup());

    JPanel buttonPanel = new JPanel();
    buttonPanel.add(speechButton);
    buttonPanel.add(hangupButton);

    JPanel microphonePanel = new JPanel();
    microphonePanel.setLayout(new BorderLayout());
    microphonePanel.add(new JLabel("Microphone:"),
        BorderLayout.NORTH);
    microphonePanel.add(microphoneField, BorderLayout.CENTER);
    microphonePanel.add(buttonPanel, BorderLayout.SOUTH);

    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.add(speakerPanel, BorderLayout.NORTH);
    frame.add(keyPanel, BorderLayout.CENTER);
    frame.add(microphonePanel, BorderLayout.SOUTH);

    frame.pack();
    frame.setVisible(true);
  }

  /**
      Give instructions to the mail system user.
   */
  public void speak(String output)
  {
    speakerField.setText(output);
  }

  public void run(Connection c)
  {
    connect = c;
  }

  private JTextArea speakerField;
  private Connection connect;
}

Custom Layout Manager [34/72]

Form layout
Odd-numbered components right aligned
Even-numbered components left aligned
Implement LayoutManager interface type

The LayoutManager Interface Type [35/72]

public interface LayoutManager 
{ 
   void layoutContainer(Container parent); 
   Dimension minimumLayoutSize(Container parent); 
   Dimension preferredLayoutSize(Container parent); 
   void addLayoutComponent(String name, Component comp); 
   void removeLayoutComponent(Component comp); 
}

Form Layout [36/72]

Note: Can use GridBagLayout to achieve the same effect

file:horstmann/ch05_layout/FormLayout.java [source] [doc-public] [doc-private]

package horstmann.ch05_layout;
import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Insets;
import java.awt.LayoutManager;

/**
   A layout manager that lays out components along a central axis
 */
public class FormLayout implements LayoutManager
{
  public Dimension preferredLayoutSize(Container parent)
  {
    Component[] components = parent.getComponents();
    left = 0;
    right = 0;
    height = 0;
    for (int i = 0; i < components.length; i += 2)
    {
      Component cleft = components[i];
      Component cright = components[i + 1];

      Dimension dleft = cleft.getPreferredSize();
      Dimension dright = cright.getPreferredSize();
      left = Math.max(left, dleft.width);
      right = Math.max(right, dright.width);
      height = height + Math.max(dleft.height,
          dright.height);
    }
    return new Dimension(left + GAP + right, height);
  }

  public Dimension minimumLayoutSize(Container parent)
  {
    return preferredLayoutSize(parent);
  }

  public void layoutContainer(Container parent)
  {
    preferredLayoutSize(parent); // Sets left, right

    Component[] components = parent.getComponents();

    Insets insets = parent.getInsets();
    int xcenter = insets.left + left;
    int y = insets.top;

    for (int i = 0; i < components.length; i += 2)
    {
      Component cleft = components[i];
      Component cright = components[i + 1];

      Dimension dleft = cleft.getPreferredSize();
      Dimension dright = cright.getPreferredSize();

      int height = Math.max(dleft.height, dright.height);

      cleft.setBounds(xcenter - dleft.width, y + (height
          - dleft.height) / 2, dleft.width, dleft.height);

      cright.setBounds(xcenter + GAP, y + (height
          - dright.height) / 2, dright.width, dright.height);
      y += height;
    }
  }

  public void addLayoutComponent(String name, Component comp)
  {}

  public void removeLayoutComponent(Component comp)
  {}

  private int left;
  private int right;
  private int height;
  private static final int GAP = 6;
}

file:horstmann/ch05_layout/FormLayoutTester.java [source] [doc-public] [doc-private]

package horstmann.ch05_layout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;

public class FormLayoutTester
{
  public static void main(String[] args)
  {
    JFrame frame = new JFrame();
    frame.setLayout(new FormLayout());
    frame.add(new JLabel("Name"));
    frame.add(new JTextField(15));
    frame.add(new JLabel("Address"));
    frame.add(new JTextField(20));
    frame.add(new JLabel("City"));
    frame.add(new JTextField(10));
    frame.add(new JLabel("State"));
    frame.add(new JTextField(2));
    frame.add(new JLabel("ZIP"));
    frame.add(new JTextField(5));
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setVisible(true);
  }
}

Strategy Pattern [37/72]

Pluggable strategy for layout management
Layout manager object responsible for executing concrete strategy
Generalizes to Strategy Design Pattern

Other manifestation: Comparators

Comparator<Country> comp = new CountryComparatorByName();
Collections.sort(countries, comp);

Strategy Pattern [38/72]

Context

A class can benefit from different variants for an algorithm
Clients sometimes want to replace standard algorithms with custom versions

Solution

Define an interface type that is an abstraction for the algorithm
Actual strategy classes realize this interface type.
Clients can supply strategy objects
Whenever the algorithm needs to be executed, the context class calls the appropriate methods of the strategy object

Strategy Pattern [39/72]

Strategy Pattern: Layout Management [40/72]

Name in Design Pattern	Actual Name (layout management)
Context	Container
Strategy	LayoutManager
ConcreteStrategy	a layout manager such as `BorderLayout`
doWork()	a method such as `layoutContainer`

Strategy Pattern: Sorting [41/72]

Name in Design Pattern	Actual Name (sorting)
Context	Collections
Strategy	Comparator
ConcreteStrategy	a class that implements `Comparator`
doWork()	`compare`

Containers and Components [42/72]

Containers collect GUI components
Sometimes, want to add a container to another container
Container should be a component
Composite design pattern
Composite method typically invoke component methods
E.g. Container.getPreferredSize invokes getPreferredSize of components

Composite Pattern [43/72]

Context

Primitive objects can be combined to composite objects
Clients treat a composite object as a primitive object

Solution

Define an interface type that is an abstraction for the primitive objects
Composite object collects primitive objects
Composite and primitive classes implement same interface type.
When implementing a method from the interface type, the composite class applies the method to its primitive objects and combines the results

Composite Pattern [44/72]

Composite Pattern [45/72]

Name in Design Pattern	Actual Name (AWT components)
Primitive	Component
Composite	Container
Leaf	a component without children (e.g. `JButton`)
method()	a method of `Component` (e.g. `getPreferredSize`)

Scroll Bars [46/72]

Scroll bars can be attached to components
Approach #1: Component class can turn on scroll bars
Approach #2: Scroll bars can surround component
```
JScrollPane pane = new JScrollPane(component);
```
Swing uses approach #2
JScrollPane is again a component

Scroll Bars [47/72]

Decorator Pattern [48/72]

Context

Component objects can be decorated (visually or behaviorally enhanced)
The decorated object can be used in the same way as the undecorated object
The component class does not want to take on the responsibility of the decoration
There may be an open-ended set of possible decorations

Decorator Pattern [49/72]

Solution

Define an interface type that is an abstraction for the component
Concrete component classes realize this interface type.
Decorator classes also realize this interface type.
A decorator object manages the component object that it decorates
When implementing a method from the component interface type, the decorator class applies the method to the decorated component and combines the result with the effect of the decoration.

Decorator Pattern [50/72]

Decorator Pattern: Scroll Bars [51/72]

Name in Design Pattern	Actual Name (scroll bars)
Component	Component
ConcreteComponent	JTextArea
Decorator	JScrollPane
method()	a method of `Component` (e.g. `paint`)

Streams [52/72]

InputStreamReader reader = new InputStreamReader(System.in); 
BufferedReader console = new BufferedReader(reader);

BufferedReader takes a Reader and adds buffering
Result is another Reader: Decorator pattern
Many other decorators in stream library, e.g. PrintWriter

Decorator Pattern: Input Streams [53/72]

Name in Design Pattern	Actual Name (input streams)
Component	Reader
ConcreteComponent	InputStreamReader
Decorator	BufferedReader
method()	read

How to Recognize Patterns [54/72]

Look at the intent of the pattern
E.g. COMPOSITE has different intent than DECORATOR
Remember common uses (e.g. STRATEGY for layout managers)
Not everything that is strategic is an example of STRATEGY pattern
Use context and solution as "litmus test"

Litmus Test [55/72]

Can add border to Swing component

Border b = new EtchedBorder()
component.setBorder(b);

Undeniably decorative
Is it an example of DECORATOR?

Litmus Test [56/72]

Component objects can be decorated (visually or behaviorally enhanced)
PASS
The decorated object can be used in the same way as the undecorated object
PASS
The component class does not want to take on the responsibility of the decoration
FAIL--the component class has setBorder method
There may be an open-ended set of possible decorations

Putting Patterns to Work [57/72]

Invoice contains line items
Line item has description, price
Interface type LineItem
Product is a concrete class that implements this interface

file:horstmann/ch05_invoice/LineItem.java [source] [doc-public] [doc-private]

package horstmann.ch05_invoice;
/**
   A line item in an invoice.
 */
public interface LineItem
{
  /**
      Gets the price of this line item.
      @return the price
   */
  double getPrice();
  /**
      Gets the description of this line item.
      @return the description
   */
  String toString();
}

file:horstmann/ch05_invoice/Product.java [source] [doc-public] [doc-private]

package horstmann.ch05_invoice;
/**
   A product with a price and description.
 */
public class Product implements LineItem
{
  /**
      Constructs a product.
      @param description the description
      @param price the price
   */
  public Product(String description, double price)
  {
    this.description = description;
    this.price = price;
  }
  public double getPrice() { return price; }
  public String toString() { return description; }
  private String description;
  private double price;
}

Bundles [58/72]

Bundle = set of related items with description+price
E.g. stereo system with tuner, amplifier, CD player + speakers
A bundle has line items
A bundle is a line item
COMPOSITE pattern
(look at getPrice)

file:horstmann/ch05_invoice/Bundle.java [source] [doc-public] [doc-private]

package horstmann.ch05_invoice;
import java.util.ArrayList;

/**
   A bundle of line items that is again a line item.
 */
public class Bundle implements LineItem
{
  /**
      Constructs a bundle with no items.
   */
  public Bundle() { items = new ArrayList<LineItem>(); }

  /**
      Adds an item to the bundle.
      @param item the item to add
   */
  public void add(LineItem item) { items.add(item); }

  public double getPrice()
  {
    double price = 0;

    for (LineItem item : items)
      price += item.getPrice();
    return price;
  }

  public String toString()
  {
    String description = "Bundle: ";
    for (int i = 0; i < items.size(); i++)
    {
      if (i > 0) description += ", ";
      description += items.get(i).toString();
    }
    return description;
  }

  private ArrayList<LineItem> items;
}

Bundles [59/72]

Discounted Items [60/72]

Store may give discount for an item
Discounted item is again an item
DECORATOR pattern
(look at getPrice)
Alternative design: add discount to LineItem

file:horstmann/ch05_invoice/DiscountedItem.java [source] [doc-public] [doc-private]

package horstmann.ch05_invoice;
/**
   A decorator for an item that applies a discount.
 */
public class DiscountedItem implements LineItem
{
  /**
      Constructs a discounted item.
      @param item the item to be discounted
      @param discount the discount percentage
   */
  public DiscountedItem(LineItem item, double discount)
  {
    this.item = item;
    this.discount = discount;
  }

  public double getPrice()
  {
    return item.getPrice() * (1 - discount / 100);
  }

  public String toString()
  {
    return item.toString() + " (Discount " + discount
        + "%)";
  }

  private LineItem item;
  private double discount;
}

Discounted Items [61/72]

Model/View Separation [62/72]

GUI has commands to add items to invoice
GUI displays invoice
Decouple input from display
Display wants to know when invoice is modified
Display doesn't care which command modified invoice
OBSERVER pattern

Change Listeners [63/72]

Use standard ChangeListener interface type
public interface ChangeListener { void stateChanged(ChangeEvent event); }
Invoice collects ArrayList of change listeners
When the invoice changes, it notifies all listeners:
ChangeEvent event = new ChangeEvent(this); for (ChangeListener listener : listeners) listener.stateChanged(event);

Change Listeners [64/72]

Display adds itself as a change listener to the invoice

Display updates itself when invoice object changes state

final Invoice invoice = new Invoice();
final JTextArea textArea = new JTextArea(20, 40);
ChangeListener listener = new
   ChangeListener()
   {
      public void stateChanged(ChangeEvent event)
      {
         textArea.setText(...);
      }
   };

Observing the Invoice [65/72]

Iterating Through Invoice Items [66/72]

Invoice collect line items
Clients need to iterate over line items
Don't want to expose ArrayList
May change (e.g. if storing invoices in database)
ITERATOR pattern

Iterators [67/72]

Use standard Iterator interface type
public interface Iterator<LineItem>
{
   boolean hasNext();
   LineItem next();
   void remove();
}
remove is "optional operation" (see ch. 8)
implement to throw UnsupportedException
implement hasNext/next manually to show inner workings

file:horstmann/ch05_invoice/Invoice.java [source] [doc-public] [doc-private]

package horstmann.ch05_invoice;
import java.util.ArrayList;
import java.util.Iterator;

import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

/**
   An invoice for a sale, consisting of line items.
 */
public class Invoice
{
  /**
      Constructs a blank invoice.
   */
  public Invoice()
  {
    items = new ArrayList<LineItem>();
    listeners = new ArrayList<ChangeListener>();
  }

  /**
      Adds an item to the invoice.
      @param item the item to add
   */
  public void addItem(LineItem item)
  {
    items.add(item);
    // Notify all observers of the change to the invoice
    ChangeEvent event = new ChangeEvent(this);
    for (ChangeListener listener : listeners)
      listener.stateChanged(event);
  }

  /**
      Adds a change listener to the invoice.
      @param listener the change listener to add
   */
  public void addChangeListener(ChangeListener listener)
  {
    listeners.add(listener);
  }

  /**
      Gets an iterator that iterates through the items.
      @return an iterator for the items
   */
  public Iterator<LineItem> getItems()
  {
    return new
        Iterator<LineItem>()
    {
      public boolean hasNext()
      {
        return current < items.size();
      }

      public LineItem next()
      {
        return items.get(current++);
      }

      public void remove()
      {
        throw new UnsupportedOperationException();
      }

      private int current = 0;
    };
  }

  public String format(InvoiceFormatter formatter)
  {
    String r = formatter.formatHeader();
    Iterator<LineItem>iter = getItems();
    while (iter.hasNext())
      r += formatter.formatLineItem(iter.next());
    return r + formatter.formatFooter();
  }

  private ArrayList<LineItem> items;
  private ArrayList<ChangeListener> listeners;
}

Iterators [68/72]

Formatting Invoices [69/72]

Simple format: dump into text area
May not be good enough,
E.g. HTML tags for display in browser
Want to allow for multiple formatting algorithms
STRATEGY pattern

Formatting Invoices [70/72]

file:horstmann/ch05_invoice/InvoiceFormatter.java [source] [doc-public] [doc-private]

package horstmann.ch05_invoice;
/**
   This interface describes the tasks that an invoice
   formatter needs to carry out.
 */
public interface InvoiceFormatter
{
  /**
      Formats the header of the invoice.
      @return the invoice header
   */
  String formatHeader();

  /**
      Formats a line item of the invoice.
      @return the formatted line item
   */
  String formatLineItem(LineItem item);

  /**
      Formats the footer of the invoice.
      @return the invoice footer
   */
  String formatFooter();
}

file:horstmann/ch05_invoice/SimpleFormatter.java [source] [doc-public] [doc-private]

package horstmann.ch05_invoice;
/**
   A simple invoice formatter.
 */
public class SimpleFormatter implements InvoiceFormatter
{
  public String formatHeader()
  {
    total = 0;
    return "     I N V O I C E\n\n\n";
  }

  public String formatLineItem(LineItem item)
  {
    total += item.getPrice();
    return (String.format(
        "%s: $%.2f\n",item.toString(),item.getPrice()));
  }

  public String formatFooter()
  {
    return (String.format("\n\nTOTAL DUE: $%.2f\n", total));
  }

  private double total;
}

file:horstmann/ch05_invoice/InvoiceTester.java [source] [doc-public] [doc-private]

package horstmann.ch05_invoice;
import java.awt.BorderLayout;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.event.ChangeListener;

/**
   A program that tests the invoice classes.
 */
public class InvoiceTester
{
  public static void main(String[] args)
  {
    final Invoice invoice = new Invoice();
    final InvoiceFormatter formatter = new SimpleFormatter();

    // This text area will contain the formatted invoice
    final JTextArea textArea = new JTextArea(20, 40);

    // When the invoice changes, update the text area
    ChangeListener listener = event -> textArea.setText(invoice.format(formatter));
    invoice.addChangeListener(listener);

    // Add line items to a combo box
    final JComboBox<LineItem> combo = new JComboBox<>();
    Product hammer = new Product("Hammer", 19.95);
    Product nails = new Product("Assorted nails", 9.95);
    combo.addItem(hammer);
    Bundle bundle = new Bundle();
    bundle.add(hammer);
    bundle.add(nails);
    combo.addItem(new DiscountedItem(bundle, 10));

    // Make a button for adding the currently selected
    // item to the invoice
    JButton addButton = new JButton("Add");
    addButton.addActionListener(event -> {
      LineItem item = (LineItem) combo.getSelectedItem();
      invoice.addItem(item);
    });

    // Put the combo box and the add button into a panel
    JPanel panel = new JPanel();
    panel.add(combo);
    panel.add(addButton);

    // Add the text area and panel to the content pane
    JFrame frame = new JFrame();
    frame.add(new JScrollPane(textArea),
        BorderLayout.CENTER);
    frame.add(panel, BorderLayout.SOUTH);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setVisible(true);
  }
}

Formatting Invoices [71/72]

Formatting Invoices [72/72]

Revised: 2007/09/11 16:27