Java Look-and-Feel Design Guidelines – Part IV

Eileen KraemerUniversity of GeorgiaCSCI 4800/600

Previously, we talked about …

Applet v. Application Placement of applets

Designing for accessibility Checking for accessibility Usability testing

Internationalization / localization Creating/using resource bundles

Designing for accessibility

Provide accessible names, accessible descriptions Use mnemonics and keyboard shortcuts All interface components must be keyboard traversable

Assign initial keyboard focus Specify tab traversal order

Don’t customize fonts or colors unnecessarily If necessary, use properties to specify colors, fonts Use dynamic GUI layout Custom components must implement accessible

Now, …

… let’s look at the “nuts and bolts” of accomplishing these goals

The Java Accessibility API (JAAPI)

standard extension in all releases of the Java 2 platform component can utilize this extension by implementing the Accessible

interface only one method call: getAccessibleContext() returns an instance of AccessibleContext

specific to the component provides the info and functionality to enable accessibility

AccessibleContext info about the component's role (button, checkbox, etc.) accessible name (more on this soon) Number of children, & more Can generate accessibility events when a noteworthy event has occurred.

All of the standard JFC/Swing components implement the Accessible interface

Accessible name, description: how used

accessible name succinct explanation of component’s purpose assistive technology will often present (speak) the

name of each component encountered by a user

accessible description more verbose explanation provide in cases where additional info needed assistive tech retrieves when user requests it

Accessible name: how to set

JFC/Swing components with non-editable text (menu items, buttons, etc.) have accessible name set automatically

Other components need to have accessible name set by developer If the component has a label:

JTextField text = new JTextField(20); JLabel label = new Label("Address Line 1"); label.setLabelFor(text); // ... Add the text and label to a Container

For ImageIcons , create using:

ImageIcon(URL url, String name);

Accessible description: how to set

Accessible descriptions set automatically by setting tooltiptext:

JComponent.setTooltipText( )

If component has no label or tooltip, directly set name & description: permanently overrides values pulled from label or tooltip

AccessibleContext context = component.getAccessibleContext(); context.setAccessibleName("Zip"); context.setAccessibleDescription("Recipient's Zip Code");

Don’t Customize Fonts or Colors Unnecessarily

JFC/Swing components/ applications automatically inherit font and color properties from desktop and user prefs.

In most cases, get good results by accepting user's preferences.  

But, if you have to specify colors and fonts …. Use a properties file Example:

want flight simulator to have a red "stop" button in Western countries

define a property, store it in a file, flightsim.properties:

flightsim.stop.color=#ff0000

Then, use the properties:

The program can load properties file as a ResourceBundle:

ResourceBundle resources = null;Color stopColor = Color.red; // the defaulttry { resources=ResourceBundle.getBundle("flightsim");String colorString =

resources.getString("flightsim.stop.color"); stopColor = Color.decode(colorString); // the specified}catch (MissingResourceException missingException) {

// Report the error, according to severity } // stopColor has now been customized

Use Dynamic GUI Layout

Don’t call setSize() with constant values. defeats dynamic layout resulting application won’t adapt properly to users' settings.

Instead, adjust the size of each JFrame, JDialog, and JWindow at creation and each time its contents change

window.setSize(window.getPreferredSize());

allows all nested layout managers to affect the size and position of each object at runtime.

If component’s preferred size is not acceptable(rare), call setSize() with a value between getMinimumSize() and getMaximumSize().

Dynamic LayoutManagers

position graphical objects relative to each other changes in size are handled automatically components never obscure one another.

All JFC/Swing layout managers are dynamic (BorderLayout, FlowLayout, GridBagLayout, etc.)

setLayout(null); // Don’t do this!!

Requires manually setting (x,y) of every component. interface won’t work right with many accessibility options,

internationalization , user-defined preferences.

Custom Layout Managers

Implement LayoutManager2 interface (old LayoutManager interface is obsolete). Components should be positioned relative to

each other when the toolkit invokes layoutContainer() on the custom layout manager.

All Interface Components Must Be Keyboard Traversable … because many people can’t use a

pointing device effectively

Pressing tab key should move input focus from component to component

shift-tab should move focus in opposite direction.

How to implement? default FocusManager sets focus order : left-to-right and

top-to-bottom. If component shouldn’t receive input focus, create a

subclass and override isFocusTraversable() to return false.

Invoke setNextFocusableComponent() on each JComponent to "hard-wire" the focus traversal order. Messy to do this on some components and have others use the

default ordering. If used, invoke on all JComponents in a window.

Implement a subclass of java.awt.FocusManager and install it with the static method FocusManager.setCurrentManager().

Use Mnemonics

Mnemonics underlined characters that appear in menu items and on the buttons in some dialog

boxes. can only be activated when the item is visible and does not require a modifier key

(e.g., the user does not need to press the Alt key). If keyboard use is to be practical, then All menu items must have mnemonics

menu = new JMenu(); menu.setText(resources.getString("fileMenu.label")); menu.setMnemonic( resources.getString("fileMenu.mnemonic").charAt(0));

item = new JMenuItem();…

item.setMnemonic( resources.getString("menuitem.file.new.mnemonic").charAt(0));

…

Use Accelerators

displayed on menu items or buttons in parentheses after the item's text [e.g., "Save (Ctrl+S)"].

requires the use of a modifier key can be activated any time the application's window has

the input focus. …

item = new JMenuItem(); item.setAccelerator(KeyStroke.getKeyStroke( resources.getString("menuitem.file.new.accelerator")));

…

Custom Components Must Implement Accessible All standard JComponent subclasses implement this interface and do

everything necessary to be accessible All custom components should extend a standard class as far down the

JFC/Swing inheritance hierarchy as possible. For example, you want round buttons

First try to extend JButton, override all paint methods, add support for any new properties.

If JButton is too restrictive, then try to extend JButton's superclass, AbstractButton.

Only if AbstractButton is too restrictive should you extend directly from JComponent.

JComponent doesn’t implement Accessible, so subclass must do more work to work w/ assistive technologies. Some methods do exist in JComponent to help: getAccessibleParent() and

getAccessibleName() will work properly for most JComponent subclasses, with no additional code (other than 'implements Accessible').

Custom components, continued

must express its accessible role as specifically as possible. See: http://java.sun.com/j2se/1.4.2/docs/api/javax/accessibility/AccessibleContext.html

Each JFC/Swing class contains a protected inner class that actually does the accessibility work, and the root class is JComponent.AccessibleJComponent To extend accessibility behavior of subclass, create a protected

inner class that extends the inner class of the superclass override getAccessibleContext() to create an instance of this

new accessibility class.

Example

public class WarningLight extends JComponent implements Accessible {

public AccessibleContext getAccessibleContext() { // variable accessibleContext is protected in superclass

if (accessibleContext == null) { accessibleContext = new AccessibleWarningLight();} return accessibleContext;

} protected class AccessibleWarningLight extends AccessibleJComponent {

public AccessibleRole getAccessibleRole() { return AccessibleRole.ALERT;

} … // Implementation of WarningLight omitted...}

Test Cases

1. Don't touch your mouse Bring up each window and popup in your application

and attempt to visit every component using only the Tab key on the keyboard.

Use the application without touching the mouse Verify that:

Application’s features are all available Frequently-used functionality is directly accessible via an

accelerator All menu items have mnemonics  

Test Cases

2. Change the default font and colorChoose a font of 24 points or larger, and

colors other than the default. Bring up each window of the application and

verify that screen objects do not overlap and that the colors are correct.

If overlapping occurs, check the code that interacts with the LayoutManager in that window.  

Test Cases

Try using a low-vision look-and-feel Here’s a sample LowVisionMetalLookAndFeel.java Compile the file Add this code to your application:

import LowVisionMetalLookAndFeel; // ... code omitted try

{ UIManager.setLookAndFeel("LowVisionMetalLookAndFeel");} catch (Exception ex) {

System.out.println("Failed loading Low Vision Metal Look and Feel");

ex.printStackTrace(System.out); }

Test Cases

3. Use a screen reader Download and install a trial version of a screen reader that works

with Java applications, (more/better links coming soon) http://cap.ic.gc.ca/english/learning.html

Bring up each window in your application and tab to every component, verifying that you hear a reasonable description of each component as it receives the input focus.

Turn your display off. Try to use your application in this mode, accessing both core

functionality and more lightly-used features.

Internationalization

Identify Culturally Dependent Data Isolate Translatable Text in Resource

Bundles Deal with Compound Messages Format Dates and Times Use Unicode Character Properties Compare Strings Properly Convert Non-Unicode Text

Nuts and Bolts …

Creating and accessing resource bundles …

ResourceBundle objects contain locale-specific objects.

When you need a locale-specific object, you fetch it from a ResourceBundle, which returns the object that matches the end user's Locale.

The ResourceBundle Class

each ResourceBundle is a set of related subclasses that share the same base name.

Example:ButtonLabel // base_name

ButtonLabel_de // with language code

ButtonLabel_en_GB // with language and country codes

ButtonLabel_fr_CA_UNIX // with lang, country, and variant codes

To select a ResourceBundle

invoke the ResourceBundle.getBundle method.

Example:Locale currentLocale = new Locale("fr", "CA", "UNIX"); ResourceBundle introLabels = ResourceBundle.getBundle(“ButtonLabel”, currentLocale);