GUI Components: Part 2 - Java: How to Program Early Objects - page 916

(lines 28-31) that returns the preferred width and height of an OvalPanel and a getMin-
imumSize method (lines 34-37) that returns an OvalPanel 's minimum width and height.
Methods getPreferredSize and getMinimumSize are used by some layout managers to
determine the size of a component.
Class SliderFrame (Fig. 22.3) creates the JSlider that controls the diameter of the
circle. Class SliderFrame 's constructor (lines 17-45) creates OvalPanel object myPanel
(line 21) and sets its background color (line 22). Lines 25-26 create JSlider object diam-
eterJSlider to control the diameter of the circle drawn on the OvalPanel . The JSlider
constructor takes four arguments. The first specifies the orientation of diameterJSlider ,
which is HORIZONTAL (a constant in interface SwingConstants ). The second and third
arguments indicate the minimum and maximum integer values in the range of values for
this JSlider . The last argument indicates that the initial value of the JSlider (i.e., where
the thumb is displayed) should be 10 .
Lines 27-28 customize the appearance of the JSlider . Method setMajorTick-
Spacing indicates that each major tick mark represents 10 values in the range of values
supported by the JSlider . Method setPaintTicks with a true argument indicates that
the tick marks should be displayed (they aren't displayed by default). For other methods
that are used to customize a JSlider 's appearance, see the JSlider online documentation
( docs.oracle.com/javase/7/docs/api/javax/swing/JSlider.html ).
JSlider s generate ChangeEvent s (package javax.swing.event ) in response to user
interactions. An object of a class that implements interface ChangeListener (package
javax.swing.event ) and declares method stateChanged can respond to ChangeEvent s.
Lines 31-41 register a ChangeListener to handle diameterJSlider 's events. When
method stateChanged (lines 35-39) is called in response to a user interaction, line 38 calls
myPanel 's setDiameter method and passes the current value of the JSlider as an argu-
ment. JSlider method getValue returns the current thumb position.
22.3 Understanding Windows in Java
A JFrame is a window with a title bar and a border . Class JFrame is a subclass of Frame
(package java.awt ), which is a subclass of Window (package java.awt ). As such, JFrame is
one of the heavyweight Swing GUI components. When you display a window from a Java
program, the window is provided by the local platform's windowing toolkit, and therefore
the window will look like every other window displayed on that platform. When a Java
application executes on a Macintosh and displays a window, the window's title bar and
borders will look like those of other Macintosh applications. When a Java application ex-
ecutes on a Microsoft Windows system and displays a window, the window's title bar and
borders will look like those of other Microsoft Windows applications. And when a Java
application executes on a UNIX platform and displays a window, the window's title bar
and borders will look like those of other UNIX applications on that platform.
Returning Window Resources to the System
By default, when the user closes a JFrame window, it's hidden (i.e., removed from the
screen), but you can control this with JFrame method setDefaultCloseOperation . Inter-
face WindowConstants (package javax.swing ), which class JFrame implements, declares
three constants— DISPOSE_ON_CLOSE , DO_NOTHING_ON_CLOSE and HIDE_ON_CLOSE (the de-
fault)—for use with this method. Some platforms allow only a limited number of windows