Java Reference
In-Depth Information
The Model-View-Controller Pattern
★
The technique we advocated in the previous Programming Tip is an example of
a general technique known as the
Model-View-Controller
pattern. Display 17.13
gives a diagram of this pattern. The Model part of the pattern performs the heart of
the application. The View part is the output part; it displays a picture of the Model's
state. The Controller is the input part; it relays commands from the user to the Model.
Each of the three interacting parts is realized as an object with responsibility for its
own tasks. In a simple task such as the
JFrame
in Display 17.11, you can have a single
object with different methods to realize each of the roles Model, View, and Controller.
To simplify the discussion, we have presented the Model-View-Controller pattern as if
the user interacts directly with the Controller. The Controller need not be under the direct
control of the user, but could be controlled by some other software or hardware component.
In a Swing GUI, the View and Controller parts might be separate classes or separate methods
combined into one larger class that displays a single window for all user interactions.
Model-View-
Controller
Self-Test Exercises
23. Suppose you omit the method
actionPerformed
from the class in Display 17.11
and make no other changes. Would the class compile? If it compiles, will it run
with no error messages?
24. Suppose you omit the method
actionPerformed
and the phrase
implements
ActionListener
from the class in Display 17.11 and make no other changes.
Would the class compile? If it compiles, will it run with no error messages?
The Model-View-Controller Pattern
Display 17.13
Model
data1
data2
.
.
.
Manipulate
Notify
View
Controller
...
...
update()
...
...
