Graphical User Interfaces in Java Part 2

Size: px

Start display at page:

Download "Graphical User Interfaces in Java Part 2"

Flora Singleton
5 years ago
Views:

1 Graphical User Interfaces in Java Part 2 COMP440 Penn State Harrisburg April 17, 2007 Julia M. Lobur 1 Objectives Illustrate Swing look-and-feel. Demonstrate the relationship between concurrency and Java Swing. Present Java Beans. Discuss alternatives to Swing. 2 1

2 Look and Feel Java employs a pluggable look and feel (PLAF) model to control the appearance of a UI. You can set the LAF in your program or use getsystemlookandfeelclassname() method for consistency. You can write your own LAF by implementing the abstract class LookAndFeeland utilizing methods from the javax.swing.plaf package. 3 Look and Feel Three main LAFs are built into javax.swing.plaf: Windows windows.windowslookandfeel Motif motif.motiflookandfeel Metal (cross platform) Set LAF using UIManager.setLookAndFeel("com.sun.j ava.swing.plaf.<laf>"); Demo LookAndFeel.java Pages

3 Look and Feel You can override the default look and feel at the command line: java -Dswing.defaultlaf= com.sun.java.swing.plaf. motif.motiflookandfeel <applicationname> 5 Swing and Concurrency Recall last time, we cautioned against running a GUI through a run() method. Watch what happens when this executes:... public static void main(string[] args) { run(new LongRunningTask(), 200, 150);... // LongRunningTask is a JFrame Demo LongRunningTask.java Pages

4 Swing and Concurrency The listener on Button b2 has no effect because the event dispatch queue is busy with the long running task:... b2.addactionlistener(new ActionListener() { public void actionperformed(actionevent evt) { Thread.currentThread().interrupt() ;}});... So what can be done? 7 Swing and Concurrency Why not try instantiating en ExecutorService and just shutting down the service to stop execution?... ExecutorService executor = Executors.newSingleThreadExecutor();... b2.addactionlistener(new ActionListener() { public void actionperformed(actionevent e) { executor.shutdownnow(); // Heavy-handed }}); Demo InterruptableLongRunningTask.java Pages

5 Swing and Concurrency What happens when we try to stop and start the task in InterruptableLongRunningTask more than once? Why? Demo InterruptableLongRunningTask.java Pages Swing and Concurrency The Callable/Future feature in Java 5 is what we need. Eckel defines a TaskManager class having tuples to hold the Callable and the Future that comes back from it. The tuple allows us to keep track of the original task from which we can get information not returned by Future. Demo InterruptableLongRunningCallable.java on Pages

6 Swing and Concurrency Be sure to give your user feedback if you ever need to execute a long-running background task. Examples of long-running tasks include database queries, and network-intensive processes. The MonitoredLongRunningCallable program gives you a framework that you can build upon. Demo MonitoredLongRunningCallable.java on Pages Java Beans The "visual programming" paradigm involves: A canvass upon which you can place components. A palette of components whose presentation you control through their properties. Behaviors that are connected to the components. Key idea: The IDE interrogates the components to determine the properties are available to you. 12 6

7 Java Beans You can write your own Java Beans for use in IDEs by following the naming conventions. When you do this, the Bean properties that you need to expose to the IDE will be properly flagged. These properties and methods can be interrogated by an Introspector (in addition to the IDE). Demo BeanDumper.java on Pages Java Beans For a property named xxx, you need to have getxxx() and setxxx() methods. A boolean xxx, may have isxxx(). Ordinary methods must be public. If you write a customized event, xxx, you'll need addxxxxxlistener() and removexxxlistener() methods. 14 7

8 Java Beans You can never be sure how your bean will be used. If it's in a multithreaded environment, most methods should be synchronized. If more than one listener is interested in an event, e.g., MouseListener and MouseMotionEvent, you must synchronize the methods, otherwise the results are unpredictable. 15 Java Beans A Bean needs to be packaged before a Beanenabled IDE can use it. The package is a jar file consisting of all of the Bean components and a manifest entry indicating that the jar contains a Bean. Your Bean should reside inside its own package. The manifest entry must include the package name. 16 8

9 Java Beans This is the manifest format: Manifest-Version 1.0 Name: <package>/<mainclass>.class Java-Bean: True Package it up with: jar cfm <beanname>.jar <manifestname>.mf <packagename> 17 Swing Alternatives Swing is fine for use in the enterprise. Desktops are controlled by the enterprise. Swing is seen as too heavyweight for Web applications Applets are little better. You don't have control over the desktop-- or even the browser. For Internet-based applications, a number of alternatives are gaining traction. 18 9

10 Swing Alternatives The 800 pound gorilla in the game is Adobe with its Macromedia Flex Flash solution. Just about every browser contains a Flash player. The plug-in is a small download. The IDE comes with a component library. You program the components using MXML. Macromedia XML. See Pages Swing Alternatives AJAX (Asychronous JavaScript and XML) A set of native client-side browser technologies that can be combined to build powerful user interfaces and asynchronous communication with server software. Uses the native browser scripting language: No plug-ins required. Gaining a great deal of support from major tool vendors, 20 10

11 Swing Alternatives AJAX Disadvantages: Complex: sophisticated development can be difficult. Security has not been ironed out. 21 Swing Alternatives SWT (Standard Widget Toolkit) Free GUI library from (IBM created it.) Provides responsive user experience. Virtual machine is for Windows only. Probably Linux soon

12 Swing Alternatives SWT (Standard Widget Toolkit) Free GUI library from (IBM created it.) Virtual machine is for Windows only. Probably Linux soon. SwingWT Free from swingwt.sourceforge.net. Provides a Swing compatible API, but uses SWT for the implementation. 23 Swing Alternatives BambooKit Light-weight XMLbased GUI good for small devices. Zaval Another light-weight GUI. Certainly, many more will emerge in the near future

13 Summary Swing look and feel can be controlled by your program. Java Swing concurrency is tricky. Take advantage of your author's TaskManager program as a template. Java Beans allow you to create and distribute custom graphical components. There are many alternatives to Swing, with more sure on the way

Java Swing Introduction

Course Name: Advanced Java Lecture 18 Topics to be covered Java Swing Introduction What is Java Swing? Part of the Java Foundation Classes (JFC) Provides a rich set of GUI components Used to create a Java