如何在AWT,Swing和SWT中选择？

IBM工程师写的，参见。

http://www-128.ibm.com/developerworks/opensource/library/os-swingswt/ 

AWT:

In general for AWT (and also Swing and SWT), each event type has an associated XxxListener interface (and possibly XxxAdapter null implementation), where Xxx is the event without the Event suffix (for example, KeyListener for a KeyEvent), which is used to pass the events to handlers. Applications register with the event source (the GUI component or widget) for the events they are interested in processing. Some listeners handle multiple events.

One nice feature of AWT is that it, in general, supports automatic disposal of GUI components. This means that you rarely need to dispose components. The exception is high-level components, such as Dialogs and Frames. If you create resources that consume significant host resources, you can dispose of them manually.

AWT components are thread-safe, which means you do not need to be concerned as to which thread in your application updates the GUI. This can eliminate many GUI update problems, but can make AWT GUIs run slower.

AWT allows you to build GUIs top-down or bottom-up or in any combination. By top-down, I mean creating a container component before any of its children. By bottom-up, I mean creating children before creating their containing (or parent) component. Thus, a component can exist without a parent container, and its parent can change over time.

AWT GUIs, in general, are not accessible. There is no API for an AWT programmer to specify accessibility information. Accessibility deals with how well an application can be used by people with disabilities. To be accessible an application, together with the platform it runs on, must enable PwDs to use the application with the appropriate assistive technologies (tools that provide alternate user interfaces). Many governments and corporations have standards that require applications to be enabled for accessibility.

Sun wanted the Java language to be a "write once, run everywhere" (WORE) environment. This means Java code could be developed and tested on one host (Windows®, for example) and be expected to run the same on any other Java host without testing. For the most part, Java technology succeeded, but AWT was a weak spot. Because AWT depended on host GUI peer controls (where each AWT component has a parallel host control or peer) to implement the GUI, the GUI looked and -- more importantly -- behaved differently on different hosts. This resulted in a "write once, test everywhere" (WOTE) situation, which was less than satisfactory.

AWT provides a rich graphics environment, especially in Java V1.2 and beyond. Through the Graphics2D object, and Java2D and Java3D services, many powerful graphical applications, such as drawing and charting packages and, combined with JavaSound, competitive interactive games, can be created.

Swing:

Separation of model from the view and controller

For all components with models (such as buttons, lists, tables, trees, rich text), the model is separate from the component. This allows the model to be adapted to the needs of the application and for it to be shared by multiple views. Default models per component type are provided for convenience.

Programmable look and feel

Each component's look (appearance) and feel (how it reacts to input events) is controlled by a separate and dynamically replaceable implementation. This allows the look and feel of all or part of a Swing-based GUI to change.

Renderers and editors

Most components that show model content, such as lists, tables, and trees, can process model elements of almost any type. This is done by mapping a renderer or editor for each component type and model type. For example, a table with a column containing java.util.Date values can have special code to present the date value and edit the date value. Each column can have different types.

Accessibility

Creating a GUI that is accessible to people with disabilities is important. Swing offers an extensive infrastructure and API for enabling GUIs for accessibility. This support is independent of but integrates with the host accessibility support, if any.

Like AWT, Swing supports automatic disposal of GUI components. Swing also supports the AWT bottom-up and top-down construction methods.

Unlike AWT, Swing components are not thread-safe, which means you need to be concerned as to which thread in your application updates the GUI. If you err in thread use, unpredictable behavior, including user interface glitches, can occur. Utility routines exist to help manage threading issues.

Like AWT, one of Swing's advantages is that it comes standard with Java technology. This means you do not need to install it. Unfortunately, Swing has evolved a lot, so it is easy to become dependent on features provided in more recent versions of the Java language, which may force users to upgrade their Java runtimes.

SWT is a low-level GUI tool kit comparable in concept to AWT. JFace is a set of enhanced components and utility services to make building GUIs with SWT easier. The builders of SWT learned from the AWT and Swing implementations and tried to build a system that had the advantages of both without their disadvantages. In many ways, they succeeded.

SWT is a lot like AWT in that it is based on a peer implementation. It overcomes the LCD problem faced by AWT by defining a set of controls adequate to make most office applications or developer tools and then, on a host-by-host basis, creating emulated (like Swing) controls for any not supplied by the particular host. For most modern hosts, nearly all the controls are based on native peers. This means that an SWT-based GUI has a host look and feel, and host performance. This avoids the most widely held complaints with AWT and Swing. Certain hosts have low-function controls, so SWT supplies extended, often emulated, versions (often with "C" as the first letter in their names) to allow the more generally expected behavior.

SWT is different from AWT in how the peers work. In SWT, the peers are just wrappers on host controls. In AWT, peers can provide services to minimize the differences between hosts (this is where AWT ran into a lot of its behavior issues). This means that an SWT application is really a host application, with all the good and bad points that entails. It also means that SWT does not fully achieve the WORE goal; it is more a WOTE solution. That said, SWT does a remarkable job of creating a portable solution, albeit not as well as Swing.

The SWT widgets, layouts, and events are summarized below (see Listing 7, Listing 8 and Listing 9). As you can see, these sets are far more extensive than that supplied by AWT and compares well to the Swing set.

Object    *Dialog         ColorDialog         DirectoryDialog         FileDialog         FontDialog         MessageDialog         PrintDialog     *Widget        Menu        *Item            CoolItem            !CTabItem            MenuItem            TabItem            TableColumn            TableItem            TableTreeItem            ToolItem            TrayItem            TreeColumn            TreeItem        *Control            Button            Label            ProgressBar            Sash            Scale            Scrollable                Composite                    ~Browser                    Canvas                        *~AbstractHyperlink                            ~Hyperlink                                ~ImageHyperlink                            *~ToggleHyperline                                ~TreeNode                                ~Twistie                        AnimatedProgress                        !CLabel                        Decorations                            Shell                        FormText                        StyledText                        TableCursor                    !CBanner                    !CCombo                    Combo                    CoolBar                    !CTabFolder                    ~ExpandableComposite                        ~Section                    ~FilteredList                    ~FilteredTree                    ~Form                    Group                    ~PageBook                    ProgressIndicator                    !SashForm                    !ScrolledComposite                    TabFolder                    Table                    TableTree                    ToolBar                    Tray                    Tree                    ViewForm                List                Text            Slider

NOTE: Many other SWT widgets exist in several other packages, but this is the basic set.

Like AWT and Swing layout managers, SWT provides a comprehensive set of layouts. Both layout systems, combined with nested containers, can generate almost any needed layout algorithm. All three GUI libraries also support absolute control positioning. The lack of a SWT BorderLayout equivalent is disappointing. The FormLayout is very nice for creating form-base input. I think the SWT layout scheme is a little harder to learn to use than the AWT/Swing set.

*Layout    FillLayout    FormLayout    GridLayout    RowLayout    !StackLayout

NOTE: Other SWT layout managers exist in several other packages, and many are specialized to the container they lay out, but this is the basic set.

Like the AWT and Swing event systems, SWT provides a comprehensive set of events. Although the events are not one-to-one with AWT/Swing (for example, AWT and Swing buttons both fire ActionEvent while SWT buttons fire SelectionEvent), they are generally equivalent.

Object    EventObject        SWTEventObject            TypedEvent                AimEvent                !BidiSegmentEvent                ControlEvent                !CTabFlolderEvent                DisposeEvent                DragSourceEvent                DragTargetEvent                !ExtendedModifyEvent                focusEvent                HelpEvent                KeyEvent                    TraverseEvent                    VerifyEvent                !LineBackgroundEvent                !LineStyleEvent                MenuEvent                ModifyEvent                MouseEvent                PaintEvent                SelectionEvent                    TreeEvent                ShellEvent                !TextChangedEvent                !TextChangingEvent

NOTE: Other SWT events exist in several other packages, but this is the basic set. These are specific events generated from a more generic event.

Many Swing components, such as JTable, have models. SWT control equivalents (such as Table) do not; they have items, instead. Items are generally limited to showing text or generally small images (such as icons). To provide a Swing-like model structure, JFace ContentProviders are used. These providers act as a bridge between the application-supplied model (such as a java.util.Array for a List or Table), and the control acting as the view. In order to format arbitrary model objects into items, SWT uses JFace LabelProviders, which generate a text or iconic form for any model object. This can limit the sophistication of the display of complex model objects. Other providers, such as ColorProviders and LabelDecorators, can enhance the display of items. For the special case of Tables, SWT provide a CellEditor that temporarily links an arbitrary SWT control to a Table cell to act as an editor for that cell.

SWT does not support automatic disposal of GUI controls. This means that you must explicitly dispose of any controls or resources, such as colors or fonts, you create, as opposed to getting from an API call. This effort is eased somewhat as container controls dispose of their child controls automatically.

SWT only allows you to build GUIs top-down. Thus, a control cannot exist without a parent container, and its parent cannot, in general, change over time. This approach is much less flexible than AWT/Swing. Controls are added to a parent container during creation and removed when disposed. Also, the SWT use of style bits only at construction time can limit the flexibility of some GUI controls. Many styles are hints only and do not work the same on all platforms.

Like Swing, SWT components are not thread-safe, which means you need to be concerned about which thread in your application updates the GUI. If you err in thread use an exception is thrown. I think this is better than the non-deterministic Swing approach. Special utility routines exist to help manage threading issues.

SWT GUIs are generally accessible if the supporting host provides accessibility services. SWT provides a basic out-of-process API for programmers to specify accessibility information when the default information is inadequate.

SWT provides a limited graphics environment. To date, it does not compare well to the support of Java2D and Java3D. Eclipse provides a separate feature called Graphical Editing Framework (GEF) with a component called Draw2D that can be used to create some drawing applications, such as UML modeling tools. Unfortunately, GEF is difficult to use stand-alone (meaning outside the entire Eclipse environment).

Unlike AWT and Swing, SWT and JFace do not come with Java technology. They must be installed separately, as part of an Eclipse installation or as separate libraries. The Eclipse team has made it fairly easy to install and run SWT independently of Eclipse. The needed Java archives (JAR) and Dynamic Link Libraries (DLL), and similar libraries for UNIX® and Macintosh can be downloaded separately from the Eclipse Web site. The JFace libraries require you to download all of Eclipse and copy out the needed JARs. Once downloaded, the JARs need to be on the Java CLASSPATH and the DLLs on the system PATH.

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The following table compares, in no particular order, many characteristics of the AWT, SWT, and Swing libraries. This list is not exhaustive, but covers the most important characteristics.

Function/Role/Aspect AWT Swing SWT (style) Display static text Label JLabel Label, CLabel Display multi-line static text Multiple Labels Multiple JLabels or JLabel with HTML content Multiple Labels or Label with newlines Display multi-line formatted static text Multiple Labels with different fonts JLabel with HTML content Multiple Labels with different fonts Single-line text entry TextField JTextField Text(SWT.SINGLE) Multi-line text entry TextArea JTextArea Text(SWT.MULTI) Display an image N/A JLabel Label Display text and image N/A JLabel CLabel ToolTip pop-up help N/A setToolTip on component, subclass JToolTip setToolTip on control Styled text entry N/A JEditorPane StyledText Select from list of items List JList List Simple push button with text Button JButton Button(SWT.PUSH) Simple push button with text and/or image N/A JButton Button(SWT.PUSH) Drawing area; possibly for custom controls Canvas JPanel Canvas On/off check box CheckBox JCheckBox Button(SWT.CHECK) Radio selection CheckBoxGroup ButtonGroup and menus Group and Menu Select from a drop-down list Choice JComboBox Combo, CCombo Enter text or select from a drop-down list N/A JComboBox Combo, CCombo Scrollable area ScrollPane JScrollPane Create Scrollable subclass Top level windows Dialog, Frame, Window JDialog, JFrame, JWindow Shell with different styles Generic window Window JWindow Shell Frame window Frame JFrame Shell(SWT.SHELL_TRIM) Dialog window Dialog JDialog Shell(SWT.DIALOG_TRIM) Menu Menu JMenu Menu MenuItem MenuItem JMenuItem MenuItem Menu shortcuts Generic keystrokes same as AWT host dependent mnemonics and accelerators Pop-up menu PopupMenu JPopupMenu Menu(SWT.POPUP) Menu bars MenuBar JMenuBar Menu(SWT.BAR) Display an insertion caret N/A Caret Caret Web browser N/A JTextPane (HTML 3.2) Browser (via embedded browser) Embed control in web page Applet JApplet Host control (ex. OLE) Generic container of other controls Panel JPanel Composite Generic container of other controls with a border Panel (if drawn manually) JPanel with a Border Composite(SWT.BORDER) Generic container of other controls with a border and title N/A JPanel with a TitledBorder Group Radio button (one of set on) Checkbox JRadioButton Button(SWT.RADIO) Control extent of radio buttons CheckboxGroup RadioButtonGroup Group Arrow buttons N/A JButton with image Button(SWT.ARROW) Supports int'l text orientations via ComponentOrientation same as AWT Many components support styles for this Focus Traversal Policy and Manager objects same as AWT Next on control Custom dialogs Dialog subclass JDialog subclass Dialog subclass Access to system events EventQueue services same as AWT Display services (less robust than AWT) System access dialogs FileDialog JColorChooser, JFileChooser ColorDialog, DirectoryDialog, FileDialog, FontDialog, PrintDialog Display simple message dialog N/A (must subclass Dialog) JOptionPane static methods MessageBox with numerous styles Display simple prompting dialog N/A (must subclass Dialog) JOptionPane static methods N/A (classes exist in JFace to do this) Layout managers BorderLayout, CardLayout, FlowLayout, GridLayout, GridBagLayout AWT plus BoxLayout, CenterLayout, SpringLayout FillLayout, FormLayout, GridLayout, RowLayout, StackLayout Basic drawing control Canvas JPanel Canvas Basic drawing Graphics and Graphics2D objects - Basic shapes and text, arbitrary Shapes and Strokes, Bezier, fills, etc. same as AWT GC object - Basic shapes and text Drawing transforms Affine, composites same as AWT N/A Off screen drawing BufferedImage, drawImage same as AWT Image, drawImage Double buffering Manual Automatic or manual Manual unless provided by host control Printing PrintJob and PrintGraphics same as AWT draw to Printer device Custom colors Color same as AWT Color Custom fonts Font, FontMetrics same as AWT Font Cursors selection Cursor same as AWT Cursor Image features load from file, create dynamically, extensive edits same as AWT load from file, create dynamically, basic edits Input automation Robot same as AWT N/A Display a tool bar N/A JToolBar ToolBar, CoolBar Display a progress bar N/A JProgressBar ProgressBar Divide space between areas N/A JSplitPane Sash or SashForm Display tabbed areas N/A JTabbedPane TabFolder, CTabFolder Display tabular info N/A JTable Table Format table columns N/A TableColumn TableColumn Display hierarchical info N/A JTree Tree Select from range of values N/A JSlider Slider Select from discrete range of values N/A JSpinner Scale Access to the base display Toolkit, GraphicsConfiguration, GraphicsDevice same as AWT Display Add items to the system tray N/A N/A Tray Key: N/A - Not available. In many cases, this feature can be created, with varying degrees of difficulty, by creating custom controls or containers of controls or by other custom programming.

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This article provided a comparison between the Eclipse's Standard Windows Toolkit with JFace, and the Java's Swing and Abstract Windows Toolkit GUI tool kits. Through the comparisons provided here, you can decide which GUI tool kit to use for your new applications.

In most cases, the decision is between Swing and SWT combined with JFace. In general, each of these tool kits is complete and powerful enough to build full-function GUIs, but Swing is generally superior to SWT alone (used without JFace). Swing has the advantage of being built into Java technology, is completely portable, and arguably has a better architecture. Swing also has the advantage for advanced graphical applications. SWT has the advantage of being implemented as a native application which increases the performance and native compatibility of SWT-based GUIs.

If you are developing only for one platform, SWT has an advantage in host compatibility, including integration with host features, such as use of ActiveX controls under Windows.

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Learn

• For migration of Swing to SWT, see the developerWorks tutorial "Migrate your Swing application to SWT."
  
  
• For using SWT/JFace outside of Eclipse, see the series of developerWorks articles starting with "Using the Eclipse GUI outside the Eclipse Workbench, Part 1."
  
  
• Learn more about AWT from Sun's AWT package summary documentation.
  
  
• Learn more about Swing from Sun's Swing package summary documentation. See also The Swing Connection, the Swing news page, and the tutorial Creating a GUI with JFC/Swing. For an on-line book, see O'Reilly's Java Foundation Classes in a Nutshell.
  
  
• If you're new to SWT and JFace, check out the developerWorks series "A gentle introduction to SWT and JFace," which is about creating simple SWT applications.
  
  
• Visit developerWorks' Eclipse project resources to learn more about Eclipse.
  
  
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