In general, a visual component is a composite of three distinct aspects:
• The way that the component looks when rendered on the screen
• The way that the component reacts to the user
• The state information associated with the component

No matter what architecture is used to implement a component, it must implicitly contain these three parts. Over the years, one component architecture has proven itself to be exceptionally effective: Model-View-Controller, or MVC for short. The MVC architecture is successful because each piece of the design corresponds to an aspect of a component.

In MVC terminology, the model corresponds to the state information associated with the component. For example, in the case of a check box, the model contains a field that indicates if the box is checked or unchecked. The view determines how the component is displayed on the screen, including any aspects of the view that are affected by the current state of the model. The controller determines how the component reacts to the user. For example, when the user clicks a check box, the controller reacts by changing the model to reflect the user’s choice (checked or unchecked).

 

Although the MVC architecture and the principles behind it are conceptually sound, the high level of separation between the view and the controller is not beneficial for Swing components. Instead, Swing uses a modified version of MVC that combines the view and the controller into a single logical entity called the UI delegate. For this reason, Swing’s approach is called either the Model-Delegate architecture or the Separable Model architecture. Therefore, although Swing’s component architecture is based on MVC, it does not use a classical implementation of it. Swing’s pluggable look and feel is made possible by its Model-Delegate architecture. by interfaces. To support the Model-Delegate architecture, most Swing components contain two objects. The first represents the model. The second represents the UI delegate. Models are defined by interfaces. For example, the model for a button is defined by the ButtonModel interface. UI delegates are classes that inherit ComponentUI.