Object-Oriented Programming: Inheritance - Java: How to Program Early Objects - page 390

JFrame . Class ImageIcon represents an image that can be displayed on a JLabel , and class
JFrame represents the window that will contain all the labels.
Line 13 creates a JLabel that displays its constructor argument—the string "North" .
Line 16 declares local variable labelIcon and assigns it a new ImageIcon . The constructor
for ImageIcon receives a String that specifies the path to the image. Since we specify only
a filename, Java assumes that it's in the same directory as class LabelDemo . ImageIcon can
load images in GIF, JPEG and PNG image formats. Line 19 declares and initializes local
variable centerLabel with a JLabel that displays the labelIcon . Line 22 declares and ini-
tializes local variable southLabel with a JLabel similar to the one in line 19. However,
line 25 calls method setText to change the text the label displays. Method setText can
be called on any JLabel to change its text. This JLabel displays both the icon and the text.
Line 28 creates the JFrame that displays the JLabel s, and line 30 indicates that the pro-
gram should terminate when the JFrame is closed. We attach the labels to the JFrame in
lines 34-36 by calling an overloaded version of method add that takes two parameters. The
first parameter is the component we want to attach, and the second is the region in which
it should be placed. Each JFrame has an associated layout that helps the JFrame position
the GUI components that are attached to it. The default layout for a JFrame is known as a
BorderLayout and has five regions— NORTH (top), SOUTH (bottom), EAST (right side), WEST
(left side) and CENTER . Each of these is declared as a constant in class BorderLayout . When
calling method add with one argument, the JFrame places the component in the CENTER
automatically. If a position already contains a component, then the new component takes
its place. Lines 38 and 39 set the size of the JFrame and make it visible on screen.
GUI and Graphics Case Study Exercise
9.1 Modify GUI and Graphics Case Study Exercise 8.1 to include a JLabel as a status bar that
displays counts representing the number of each shape displayed. Class DrawPanel should declare a
method that returns a String containing the status text. In main , first create the DrawPanel , then
create the JLabel with the status text as an argument to the JLabel 's constructor. Attach the JLabel
to the SOUTH region of the JFrame , as shown in Fig. 9.14.
Fig. 9.14 | JLabel displaying shape statistics.