A first GUI - An Introduction to Graphical User Interfaces with Java Swing - page 24

Frame

Titlebar

Down

Up 14

Button Label Button

Figure 3.1 The specification of the layout for the counter GUI

increment - increments the value of the counter by 1.

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decrement - decrements the value of the counter by 1.

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reset - sets the value of the counter to 0.

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getValue - returns the current value of the counter. ■

Next, we specify what the graphics should look like and how it is to work. The GUI
we have in mind should display the current value of the counter and allow the user
to increment or decrement it. To this end the GUI has two buttons . Pressing the
first one (labelled 'Up'), e.g. clicking it with the mouse, will increment the counter.
Pressing the other one (labelled 'Down') will decrement the counter. Figure 3.1
shows how we want this GUI to look. This concludes the specification of the GUI's
functionality and layout.

■ 3.2 The counter model

We now implement a counter in the non-graphical class CounterModel .Acounter
has only one integer variable value which is initialized to 0 in the constructor as
required by the specification. The variable value is private so that other classes
can only manipulate it through the methods of CounterModel .Weimplemented
the four operations requested by the specification in four methods with obvious
names: increment() , decrement() , reset() and getValue() . Here is the listing
of the class:

File: its/CounterGUI/CounterModel.java

1. package its.CounterGUI;
2. public class CounterModel {
3. private int value;

4.