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ProgrammingObject-Oriented GUIs

IISwing Components and Events

SOFTENG 350 – Lecture 17

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Organizational Stuff

• Lab on Thursday 10-12. Now: GTL and FTL (CS Building)

• Next lab on 11th May: Swing exercises.– Layout manager– GUI components: lists, text, buttons, dialogs

• Lab next week, on 19th May: guided tour to JSP technology– Downloading, installing and running a Tomcat

web server– Implementing and deploying a first Java Servlet– Implementing and deploying a first Java Server

Page

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Don’t call us, we’ll call you ! Summary

The Hollywood-Principle (don’t call us we call you) means the OO call back mechanism: the way object-oriented APIs are customized by developers. The developer (i) extends API classes and overrides template methods or (ii) implements interfaces. The developer then instantiates objects and passes them in method calls to the API.

Don’t call us and we won’t call you.

With Objects, subtype polymorphism and dynamic binding OOP languages provide a typed, higher-order parameter passing mechanism. Code can be encapsulated in an object and therefore passed as a parameter in a type-safe manner.

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Don’t ask what kind !Summary

If you have some objects that are used identical but behave differently, make their classes implement a common interface. The interface can be seen as a contract or protocol the single objects adhere to. In client code that uses the objects, use the objects as objects of their common supertype. The OOP dynamic binding mechanism knows the correct type and executes the correct service. You do not have to clutter up your service code with asking for types. The defined common interface serves as an inbuilt documentation that is kept under surveillance of the OOP language type checker. You cannot introduce a new subclass without implementing all the methods of the interface.

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Partial AWT and SwingClass Hierarchy

java.lang.Object

Component MenuComponentCheckboxGroup

Button CheckboxCanvas Choice Container Label List ScrollbarTextComponent

JComponent Window

Frame

JFrame

Dialog

JDialog

PanelScrollpane

Applet

JApplet

java.awt.* javax.swing.*

JLabel JListAbstractButton

JButton

JPanel JScrollpane

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AWT vs. Swing

• AWT Abstract Windowing Toolkit– Original Java GUI toolkit– Lowest-common denominator for all Java host

environments– Java standard, e.g., works even with old Browsers – Robust / thread-safe

• SWING– Flexible, powerful, but rather complex add-on– Richer set of GUI components– Pluggable Look-and-Feel Support– Internationalization– Not thread safe

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Swing Design Principles

• A graphical user interface is built as a containment hierarchy of GUI components

• Model Concept. Data displayed by a GUI component (so called model) are cleanly separated from their screen presentation (so called view)

• Events / Event Listeners / Event Objects. Defined Events that stem from human computer interaction (a window has been moved, the mouse has been clicked) trigger event listeners. Information about the triggering event is submitted to the event listener as an event object.

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The Initial Swing GUIContainment Hierarchy

aTopLevelContainer:JFrame or JDialog or JApplet

rootPane:JRootPane

(JPanel) glassPane:java.awt.Component

(JPanel) contentPane:java.awt.Container

layeredPane:JLayeredPane

menuBar:JMenuBar

optional

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The Initial Swing GUIContainment Hierarchy

File EditUndoRedoCut

Frame / Dialog / Applet

Root Pane

Layered Pane

Content Pane

Glass Pane

a 3D model enables menus to pop up above the content pane

allows for interception of mouse events and painting across GUI components

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Concrete ExampleContainment Hierarchy

JMenu fileMenu = new JMenu("File"); fileMenu.add("New"); fileMenu.add("Open"); fileMenu.add("Close"); JMenu editMenu = new JMenu("Edit"); editMenu.add("Undo"); editMenu.add("Redo"); editMenu.add("Cut");

JMenuBar mymenubar = new JMenuBar(); mymenubar.add(fileMenu); mymenubar.add(editMenu); JFrame myframe = new JFrame("My Frame"); myframe.setJMenuBar(mymenubar);

File EditUndoRedoCut

File EditNewOpenClose

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Swing Components

• Top-Level Containers• General-Purpose Containers • Special-Purpose Containers • Basic Controls• Text Components• Uneditable Information Displays • Interactive Displays of Highly Formatted

Information

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Top-Level Containers

JFrame. Full GUI application

JDialog. For the creation of customized Dialogs. For standardized dialogs use JOption pane instead.

JApplet

• GUI components that are on the top of a containment hierarchy

• Top-level containers do not inherit from JComponent

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General-Purpose Containers

JPanel

JScrollPane

JSplitPane

JTabbedPane

JToolBar

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Special-Purpose Containers

JInternalFrame

JLayeredPane

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Basic Controls

JButton

JCheckbox

JRadioButton and ButtonGroup

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Basic Controls

Combobox

List

Menu

Slider

Spinner

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Text Components

• Text Controls:– JTextField– JPasswordField– JFormattedTextField

• Plain Text Areas: JTextArea• Styled Text Areas:

– JEditorPane– JTextPane

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UneditableInformation Displays

JLabel

JToolTip

JProgressBar

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Interactive Displays of Highly Formatted Information

JColorChooser JFileChooser

JTreeJTable

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Models of GUI Components

• Data displayed by a GUI component (so called model) are cleanly separated from their screen presentation (so called view)

• Origin of terminology: Model-View-Controller (Smalltalk)• A GUI component can have several models. More

precisely, a model can be:– Displayed data (e.g. list items - ListModel)– Information about state (selected item - ListSelectedModel)

• Advantages– Non-volatile concept for displayed data: no redundant

data structures are necessary– The GUI model concept is integrated with the GUI

event concept. Changes of the model trigger events and can therefore be observed in a well-defined way.

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Using Models - Example

listModel = new DefaultListModel();listModel.addElement("Alan Sommerer");….

list = new JList(listModel);

public void actionPerformed(ActionEvent e) { int index = list.getSelectedIndex(); listModel.remove(index);}

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Swing Event Concept

eventsource

eventlistener

eventobject

event

a.k.a event handlera.k.a event processing

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Swing Event Concept

aJButton anActionListeneranActionEvent

button pressed

Class ActionEvent extends AWTEvent { Object getSource() }Interface ActionListener extends EventListener { void actionPerformed(ActionEvent e) }public class SwingApplication implements ActionListener { public Component createComponents() { button.addActionListener(this); } public void actionPerformed(ActionEvent anActionEvent) { event processing code } }

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Kinds of Events

• Low-level events versus semantic events• Listeners supported by all Swing Components

– Component listener– Focus listener– Key listener– Mouse listener– Mouse-motion listener– Mouse-wheel listener

• Component specific event listeners– Action– Caret – Change – Document, undoable edit – Item– List selection– Window

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Event Adapter

• Example: MouseListener versus Mouse Adapter

void mouseClicked(MouseEvent e)

void mouseEntered(MouseEvent e)

void mouseExited(MouseEvent e)

void mousePressed(MouseEvent e)

void mouseReleased(MouseEvent e)

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Swing and Threads

• Swing is not thread-safe• There is one event-dispatching thread• The single-thread rule: once a Swing component

has been realized, all code that might affect or depend on the state of that component should be executed in the event-dispatching thread.

• The responsiveness rule: Don’t do time-consuming tasks in event listeners. Spawn new threads for those instead.

The responsiveness rule

The single-thread rule

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Exceptions to the Single-Thread Rule

• A few methods are marked in the API as being thread-safe: This method is thread safe, although most Swing methods are not.

• No contradiction to the rule: construction before the realization:

public static void main(String[] args) { JFrame f = new JFrame(); construction f.pack(); f.show();

no more construction !! } }

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Swing Thread SafetyCounterexample

public static void main( String args[ ] ){ final DefaultListModel model = new DefaultListModel(); JList list = new JList( model ); JFrame frame = new JFrame(); frame.getContentPane().add( list ); frame.setVisible( true );

new Thread(){ public void run() { setPriority( Thread.MIN_PRIORITY ); while ( true ) model.addElement("FOO"); }}.start();

new Thread(){ public void run() { setPriority( Thread.MIN_PRIORITY ); while ( true ) model.removeElement("FOO"); }}.start();}}

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Swing Thread SafetyCounterexample

Error message from the runtime system:

Exception in thread “AWT-Event-Queue-0” java.lang.ArrayIndexOutOfBoundsException: 4145 >= 4145 at java.util.Vector.elementAt(Unkown Source)

Code from the API implementation:

public synchronized Object elementAt( int index ) { if (index >= elementCount) { throw new ArrayIndexOutOfBoundsException( index + " >= " + elementCount); }}

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Submitting Code to the Event-Dispatching Thread

javax.swing.SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGUI(); } });

javax.swing.SwingUtilities.invokeAndWait(new Runnable() { public void run() { createAndShowGUI(); }});

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Directed Reading

• Using Swing Components – Using Top-Level Containers – Using Models – The JComponent Class – Using Text Components – Text Component Features – The Text Component API – How to Use Buttons, Check

Boxes, and Radio Buttons – How to Make Dialogs – How to Use Labels – How to Use Lists – How to Use Panels – How to Use Tool Tips

• Using Other Swing Features – How to Use Borders – How to Use Threads

• Laying Out Components Within a Container

– A Visual Guide to Layout Managers

– Using Layout Managers – How Layout Management Works – How to Use GridBagLayout

• Writing Event Listeners – Introduction to Event Listeners – General Information about

Writing Event Listeners – Listeners Supported by Swing

Components – Implementing Listeners for

Commonly Handled Events – How to Write an Action Listener – How to Write a List Data Listener – How to Write a Mouse Listener – How to Write a Mouse-Motion

Listener – Listener API Table

• Performing Custom Painting – How Swing Components Are

Displayed – Introduction to Painting Concepts – Implementing a Custom

Component

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Summary / Next Topics

• Summary– Don’t ask what kind / Don’t call us, we’ll call you– Containment hierarchies of GUI components– Models of Swing GUI components– Swing GUI event concept– Swing and Threads– Directed Reading

• Next lab: Swing exercises.• Next tutorial on 12th May:

– MS Visual Studio Designer– HTML WYSIWYG Editor – Basic Swing drawing– Game programming taster (timing)

• Next lecture: Programming Dynamic Web Pages• Lab next week: guided tour to JSP technology