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Easy Learn Java: Programming Articles, Examples and Tips - Page 375


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Introduction to Components

Go to all tips in Swing, AWT

Swing Components

You can draw things on the screen, but there are things that have already been made for you to put on the screen. These are called components. An example of a component is a label, button or scrollbar.

The Java Swing classes provide the tools that help you build a good graphical user interface. You've already used some of the drawing methods. In this section you will learn to use Swing components.

Some advantages of using these components are:
  • Java has already defined them along with a number of methods for customizing them.
  • They paint themselves with their own paintComponent method, and redraw themselves as necessary when their state changes.
  • They automatically position and resize themselves depending on the layout.
  • Most allow user interaction which can result in calls to your methods to process the input.

Defining your own components

The predefined Java components are adequate for all normal programming, with the one exception of drawing graphical output. In this case you want to define your own "component" that draws itself, which is easily done with a subclass of JPanel and overriding the default paintComponent method.

Examples

Some of the kinds of components that you will learn to use are JLabel, JTextField, and JButton.

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Posted by jalex on Monday, June 20, 2005 (00:00:00) (2321 reads)

GUI Structural Patterns

Go to all tips in Swing, AWT

Structuring the program - Separating the Model

In all ways of structuring a GUI program, there is one vitally important issue -- separating the code which is the essence of the problem from the user interface. This logical part is variously referred to as the model, business logic, abstraction, or document. This code must not refer to the user interface directly -- it will interact with the user interface code by returning values or invoking listeners.

Motivation. There are two compelling reasons for this separation.

  1. Lower complexity -- Programs end up being less complex and therefore easier (cheaper) to modify. For the smallest programs this may not be obvious, but the benefits show up very quickly as a program grows. This is not an advantage only in large programs.
  2. Interface Flexibility -- This allows changes to the user interface, eg, moving from Swing to SWT, or to a web interface. You should be able to use your basic logic code (if applicable) with the following interfaces.
    • GUI interface. And it should be easy to change between Swing, SWT, XML based GUI, etc.
    • Command line interface - yes, some Unix sysadmins might want to run it that way.
    • Web based interface.

Well-Known Patterns

MVC - Model-View-Controller Pattern
This classic pattern is widely used, altho the Presentation-Document pattern below is a more common (because it's simpler) choice for small programs.
  • The View component presents the output and may interact with the Model to do so.
  • The Controller component accepts user input. It typically interacts with both the View and Model.
  • The Model implements the logic, and knows nothing about the interface.
Presentation-Document Pattern
This pattern is perhaps the best choice for small GUI applications.
  • The Presentation contains all user interface code (the View and Controller).
  • The Document is the logic, model, etc.
PAC - Presentation-Abstraction-Control Pattern
This is the application of stepwise refinement to GUIs. Parts of the GUI are each implemented as in MVC, and these parts are put together using MVC. This is basically a recursively applied MVC model. It would only be used for complicated GUIs.
  • The Abstraction corresponds to the Model in MVC.
  • The PAC pattern has a hierarchy of agents, each structured in the PAC model.


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Posted by jalex on Sunday, June 19, 2005 (00:00:00) (2652 reads)

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