Graphical User Interfaces - Java - page 552

Table 14-1. Layout managers

Name Notes Default on

Flows across the container (J)Panel ,

(J)Applet

FlowLayout

Five “geographic” regions (J)Frame ,

(J)Window

BorderLayout

Regular grid (all items same size) None GridLayout

Display one of many components at a time; useful for wizard-style
layouts

None

CardLayout

Very flexible but maximally complex None GridBagLayout

Single row or column of components None

BoxLayout
(Swing)

Because we've broached the subject of layout management, I should mention that each com-
ponent has a method called getPreferredSize() , which the layout managers use in decid-
ing how and where to place components. A well-behaved component overrides this method
to return something meaningful. A button or label, for example, will indicate that it wishes to
be large enough to contain its text and/or icon, plus a bit of space for padding. And, if your
JFrame is full of well-behaved components, you can set its size to be “just the size of all in-
cluded components, plus a bit for padding,” just by calling the pack() method, which takes
no arguments. The pack() method goes around and asks each embedded component for its
preferred size (and any nested container's getPreferredSize() will ask each of its com-
ponents, and so on). The JFrame is then set to the best size to give the components their pre-
ferred sizes as much as is possible. If not using pack() , you need to call the setSize()
method, which requires either a width and a height, or a Dimension object containing this in-
formation.

A FlowLayout is the default in JPanel and Applet/JApplet . It simply lays the components
out along the “normal” axis (left to right in European and English-speaking locales, right to
left in Hebrew or Arabic locales, and so on, as set by the user's Locale settings). The overall
collection of them is centered within the window.