download Swing

of 55

  • date post

  • Category


  • view

  • download


Embed Size (px)

Transcript of Swing

Java Swing Swing was developed to provide a more sophisticated set of GUI components than the earlier Abstract Window Toolkit. Swing provides a native look and feel that emulates the look and feel of several platforms, and also supports a pluggable look and feel that allows applications to have a look and feel unrelated to the underlying platform. The Swing Architecture Swing is a platform-independent, Model-View-Controller GUI framework for Java. It follows a single-threaded programming model, and possesses the following traits: Foundations: Swing is platform independent both in terms of expression (Java) and implementation (Look-and-Feel). Extensible: Swing is a highly partitioned architecture, which allows for the "plugging" of various custom implementations of specified framework interfaces: Users can provide their own custom implementation(s) of these components to override the default implementations. In general, Swing users can extend the framework by extending existing (framework) classes and/or providing alternative implementations of core components. Swing is a component-based framework. The distinction between objects and components is a fairly subtle point: concisely, a component is a well-behaved object with a known/specified characteristic pattern of behaviour. Swing objects asynchronously fire events, have "bound" properties, and respond to a well-known set of commands (specific to the component.) Specifically, Swing components are Java Beans components, compliant with the Java Beans Component Architecture specifications. Customizable: Given the programmatic rendering model of the Swing framework, fine control over the details of rendering of a component is possible in Swing. As a general pattern, the visual representation of a Swing component is a composition of a standard set of elements, such as a "border", "inset", decorations, etc. Typically, users will programmatically customize a standard Swing component (such as a JTable) by assigning specific Borders, Colors, Backgrounds, opacities, etc., as the properties of that component. Configurable: Swing's heavy reliance on runtime mechanisms and indirect composition patterns allows it to respond at runtime to fundamental changes in its settings. For example, a Swing-based application can change its look and feel at runtime. Further, users can provide their own look and feel implementation, which allows for uniform changes in the look and feel of existing Swing applications without any programmatic change to the application code. Lightweight UI: Swing's configurability is a result of a choice not to use the native host OS's GUI controls for displaying itself. Swing "paints" its controls programmatically through the use of Java 2D APIs, rather than calling into a native user interface toolkit. Thus, a Swing component does not have a corresponding native OS GUI component, and is free to render itself in any way that is possible with the underlying graphics APIs. AWT and Swing class hierarchy Since early versions of Java, a portion of the Abstract Window Toolkit (AWT) has provided platform-independent APIs for user interface components. In AWT, each component is rendered and controlled by a native peer component specific to the underlying windowing system. By contrast, Swing components are often described as lightweight because they do not require allocation of native resources in the operating system's windowing toolkit. The AWT components are referred to as heavyweight components. Much of the Swing API is generally a complementary extension of the AWT rather than a direct replacement. In fact, every Swing lightweight interface ultimately exists within an AWT heavyweight component because all of the top-level components in Swing (JApplet, JDialog, JFrame, and JWindow) extend an AWT top-level container. If you do not explicitly add a GUI component to a container, the GUI component will not be displayed when the container appears on the screen. Swing, which is an extension library to the AWT, includes new and improved components that enhance the look and functionality of GUIs. Swing can be used to build Standalone swing gui Apps as well as Servlets and Applets. Swing is more portable and more flexible than AWT. Swing contains components that youll use to build a GUI. Here some of the commonly used Swing components. Top-Level Containers

Swing provides three generally useful top-level container classes: JFrame, JDialog, and JApplet. When using these classes, you should keep these facts in mind: To appear onscreen, every GUI component must be part of a containment hierarchy. A containment hierarchy is a tree of components that has a top-level container as its root. Each GUI component can be contained only once. If a component is already in a container and you try to add it to another container, the component will be removed from the first container and then added to the second. Each top-level container has a content pane that, contains (directly or indirectly) the visible components in that top-level container's GUI. You can optionally add a menu bar to a top-level container. The menu bar is by convention positioned within the top-level container, but outside the content pane. Some look and feels, such as the Mac OS look and feel, give you the option of placing the menu bar in another place more appropriate for the look and feel, such as at the top of the screen. The JComponent Class: With the exception of top-level containers, all Swing components whose names begin with "J" descend from the JComponent class. For example, JPanel, JScrollPane, JButton, and JTable all inherit from JComponent. However, JFrame and JDialog don't because they implement top-level containers. The JComponent class extends the Container class, which itself extends Component. The Component class includes everything from providing layout hints to supporting painting and events. The Container class has support for adding components to the container and laying them out. The JComponent class provides the following functionality to its descendants: Tool tips: By specifying a string with the setToolTipText method, you can provide help to users of a component. When the cursor pauses over the component, the specified string is displayed in a small window that appears near the component. Painting and borders The setBorder method allows you to specify the border that a component displays around its edges. To paint the inside of a component, override the paintComponent method. Application-wide pluggable look and feel: Behind the scenes, each JComponent object has a corresponding ComponentUI object that performs all the drawing, event handling, and size determination, and so on for that JComponent. Exactly which ComponentUI object is used depends on the current look and feel, which you can set using the UIManager.setLookAndFeel method. You can associate one or more properties (name/object pairs) with any JComponent. For example, a layout manager might use properties to associate a constraints object with each JComponent it manages. You put and get properties using the putClientProperty and getClientProperty methods. Support for layout: Although the Component class provides layout hint methods such as getPreferredSize and getAlignmentX, it doesn't provide any way to set these layout hints, short of creating a subclass and overriding the methods. To give you another way to set layout hints, the JComponent class adds setter methods setMinimumSize, setMaximumSize, setAlignmentX, and setAlignmentY. Support for drag and drop: The JComponent class provides API to set a component's transfer handler, which is the basis for Swing's drag and drop support. Key bindings: This feature makes components react when the user presses a key on the keyboard. For example, in many look and feels when a button has the focus, typing the Space key is equivalent to a mouse click on the button. The look and feel automatically sets up the bindings between pressing and releasing the Space key and the resulting effects on the button. Text Components Swing text components display text and optionally allow the user to edit the text. Programs need text components for tasks ranging from the straightforward (enter a word and press Enter) to the complex (display and edit styled text with embedded images in an Asian language). Swing provides six text components, along with supporting classes and interfaces that meet even the most complex text requirements. In spite of their different uses and capabilities, all Swing text components inherit from the same superclass, JTextComponent, which provides a highly-configurable and powerful foundation for text manipulation. The following figure shows the JTextComponent hierarchy.

Buttons To create a button, you can instantiate one of the many classes that descend from the AbstractButton class. The following table shows the Swing-defined AbstractButton subclasses that you might want to use: Class JButton JCheckBox JRadioButton JMenuItem JCheckBoxMenuItem JRadioButtonMenuIte m JToggleButton Summary A common button. A check box button. One of a group of radio buttons. An item in a menu. A menu item that has a check box. A menu item that has a radio button. Implements toggle functionality inherited by JCheckBox and JRadioButton. Can be instantiated or subclassed to create two-state buttons.

Swing button can display both text and an image. In most look and feels, the user can click a button by pressing the Alt key and the mnemonic. When a button is disabled, the look and feel automatically generates the button's disabled appearance. However, you could provide an image to be substituted for the normal image. For example, you could provide gray versions of the images used in the left and right buttons. How you implement event handling depends on the type of button you use and how you use it. Generally, you implement an action listener, which is notifie