Java Reference
In-Depth Information
CHAPTER 3
■ ■ ■
The Model-View-Controller
Architecture
C
hapter 2 explored how to deal with event producers and consumers with regard to Swing
components. We looked at how event handling with Swing components goes beyond the
event-handling capabilities of the original AWT components. In this chapter, we will take the
Swing component design one step further to examine what is called the Model-View-Controller
(MVC) architecture.
Understanding the Flow of MVC
First introduced in Smalltalk in the late 1980s, the MVC architecture is a special form of the
Observer pattern described in Chapter 2. The
model
part of the MVC holds the state of a
component and serves as the Subject. The
view
part of the MVC serves as the Observer of the
Subject to display the model's state. The view creates the
controller
, which defines how the
user interface reacts to user input.
MVC Communication
Figure 3-1 shows how the MVC elements communicate—in this case, with Swing's multiline
text component, the
JTextArea
. In MVC terms, the
JTextArea
serves as the view part within the
MVC architecture. Displayed within the component is a
Document
, which is the model for the
JTextArea
. The
Document
stores the state information for the
JTextArea
, such as the text contents.
Within the
JTextArea
is the controller, in the form of an
InputMap
. It maps keyboard input to
commands in an
ActionMap
, and those commands are mapped to
TextAction
objects, which
can modify the
Document
. When the modification happens, the
Document
creates a
DocumentEvent
and sends it back to the
JTextArea
.
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