GUI Components: Part 2 - Java: How to Program Early Objects - page 941

10 boxLayoutFrame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );

11 boxLayoutFrame.setSize( 400 , 220 );

12 boxLayoutFrame.setVisible( true );

13

}

14

} // end class BoxLayoutDemo

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Fig. 22.17 | Test class for BoxLayoutFrame . (Part 2 of 2.)

Creating Box Containers
Lines 19-22 create Box containers. References horizontal1 and horizontal2 are initial-
ized with static Box method createHorizontalBox , which returns a Box container with
a horizontal BoxLayout in which GUI components are arranged left-to-right. Variables
vertical1 and vertical2 are initialized with static Box method createVerticalBox ,
which returns references to Box containers with a vertical BoxLayout in which GUI com-
ponents are arranged top-to-bottom.

Struts
The loop at lines 27-28 adds three JButton s to horizontal1 . The for statement at lines
31-35 adds three JButton s to vertical1 . Before adding each button, line 33 adds a ver-
tical strut to the container with static Box method createVerticalStrut . A vertical
strut is an invisible GUI component that has a fixed pixel height and is used to guarantee
a fixed amount of space between GUI components. The int argument to method create-
VerticalStrut determines the height of the strut in pixels. When the container is resized,
the distance between GUI components separated by struts does not change. Class Box also
declares method createHorizontalStrut for horizontal BoxLayout s.