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Birds perspective on Java GUI Programming

Birds perspective on Java GUI Programming. Introduction to the major concepts. Two GUI class-libraries. AWT (Abstract Windowing Toolkit) Came first – has ”Look & Feel” as platform (Windows, Linux, Apple...) Swing Newer – common L&F across platforms L&F Programmable

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Birds perspective on Java GUI Programming

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  1. Birds perspective on Java GUI Programming Introduction to the major concepts

  2. Two GUI class-libraries • AWT (Abstract Windowing Toolkit) • Came first – has ”Look & Feel” as platform(Windows, Linux, Apple...) • Swing • Newer – common L&F across platforms • L&F Programmable • Class names mostly as AWT + ”J” in front • Not a complete replacement for AWT 02312 Indledende Datalogi

  3. Two basic App’s • Applications • Based on Frame or JFrame • Run with ”java” – to get a console (nice for debug) • Run with ”javaw” to have no console • Same ”rights” as ”native” programs • Applets • Based on Applet or JApplet • Embedded in HTML • Runs in Browser – e.g. IExplorer • Sandbox model for security (restrictions on I/O) 02312 Indledende Datalogi

  4. Applications in Swing • Your class ”extends” JFrame (inheritance)- we get a lot for free this way • The GUI is ”wired up” in the constructor • Components are added to the pane which is found with ”getContentPane()”(in AWT directly added to the Frame) • A LayoutManager places components- e.g. ”Border”, ”Grid”, ”Flow”... • E.g. in ”main” the class is instantiated 02312 Indledende Datalogi

  5. Application Code Skeleton MyClass extends JFrame { MyClass() { JButton hit = new JButton(”Hit!”); hit.<setup button+actionhandlers> getContentPane().add(hit); ....Setup Layout+more components } public static void main(String[] a){ MyClass frame = new MyClass(); frame.pack(); frame.setVisible(true);}} 02312 Indledende Datalogi

  6. From Application to Applet • Change constructor into ”void init()”- and remove calls to ”super” if any • Remove ”main” completely- no instantiation (done by browser) • No setting of tittle • Make an HTML-file with <applet > tag 02312 Indledende Datalogi

  7. The wellknown console paradigm • Client program is in charge • Client calls OS when doing I/O etc • Client continues after call • Typically asks one question at the time and waits for an answer Client OS Client OS Client time 02312 Indledende Datalogi

  8. The Event-Based Paradigm • The OS is in charge • OS calls fragments of client code - based on events • Not easy to predict calling sequences • You create code that you never call OS client client client client client time 02312 Indledende Datalogi

  9. MVC-pattern: Model-View-Control • Model is the data in e.g. attributes/fields or externally - can be complex data-structures. • View is the GUI-components setup in the constructor (Buttons, Lists, Checkboxes etc) • Control is program-flow - done via event-handlers(With MS MFC View and Control is mixed) 02312 Indledende Datalogi

  10. Listeners & Event-Handlers Appl. Comp. Event Object Listener Object The OS generates an event with help from the application’s component, and sends it to a handler. A handler is a method on a listener object Your ”listener” is registered at your component – typically in Constructor (Frame) or ”init()” (Applet) 02312 Indledende Datalogi

  11. Listener Groups • ActionListener for buttons and menus • KeyListener for keyboard • MouseListener • WindowListener for Window opened, closed etc. There are 4 ways to implement listeners & handlers…following in (personal) prioritized order 02312 Indledende Datalogi

  12. 1. Way: Inner Class • Inside the client class a new class is coded • Register listener using e.g. ”new MyListener()” • It has access to all fields in the outer class • There may be several instances of the inner class per instance of the outer class • This concept encapsulates the listeners code – without mixing MVC too much 02312 Indledende Datalogi

  13. 2. Way: Application is Listener • As with inner-class, all code is in the same file – full access to fields. • Register listener using ”this” • MVC not as mixed as anonymous classes • MVC not as separated as inner classes • Need to use ”implements” in order to extend JFrame/Frame/JApplet/Applet. ...see later slide... 02312 Indledende Datalogi

  14. 3. Way: External Class • The listener is coded in it’s own file – exactly as any other class. • Register listener using e.g. ”new MyListener()” • Control & View is completely separated- maybe too much. • No access to private fields of View class. 02312 Indledende Datalogi

  15. 4. Way: Anonymous class • The listener is registered with new without a class name at the exact place in the code where the component is inserted. • This can be done automatically by many IDE’s • This concept encapsulates the code – but mixes control and view • It is confusing and difficult to read – drop it! 02312 Indledende Datalogi

  16. Two ways to code listeners • To assure that it contains the necessary methods with the right parameters, you can use ”implements” – the drawback is that all methods (actually rather few) must be implemented. • Alternatively ”extend” an ”adapterclass”- the drawback is that it’s only possible to extend from one class 02312 Indledende Datalogi

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