AhmadLang / Java, How To Program, 2004

Figure 22.23. GridBagConstraints constants RELATIVE and REMAINDER.

(This item is displayed on pages 1043 - 1044 in the print version)

1// Fig. 22.23: GridBagFrame2.java

2// Demonstrating GridBagLayout constants.

3import java.awt.GridBagLayout;

4import java.awt.GridBagConstraints;

5import java.awt.Component;

6import javax.swing.JFrame;

7import javax.swing.JComboBox;

8import javax.swing.JTextField;

9import javax.swing.JList;

10import javax.swing.JButton;

12public class GridBagFrame2 extends JFrame

13{

14private GridBagLayout layout; // layout of this frame

15private GridBagConstraints constraints; // constraints of this layout

17// set up GUI

18public GridBagFrame2()

19{

20super( "GridBagLayout" );

21layout = new GridBagLayout();

22setLayout( layout ); // set frame layout

23constraints = new GridBagConstraints(); // instantiate constraints

25// create GUI components

26String metals[] = { "Copper", "Aluminum", "Silver" };

27JComboBox comboBox = new JComboBox( metals );

29JTextField textField = new JTextField( "TextField" );

31String fonts[] = { "Serif", "Monospaced" };T

32JList list = new JList( fonts );

34String names[] = { "zero", "one", "two", "three", "four" };

35JButton buttons[] = new JButton[ names.length ];

40// define GUI component constraints for textField

41constraints.weightx = 1;

42constraints.weighty = 1;

43constraints.fill = GridBagConstraints.BOTH;

44constraints.gridwidth = GridBagConstraints.REMAINDER;

45addComponent( textField );

46

47// buttons[0] -- weightx and weighty are 1: fill is BOTH

48constraints.gridwidth = 1;

49addComponent( buttons[ 0 ] );

50

51// buttons[1] -- weightx and weighty are 1: fill is BOTH

52constraints.gridwidth = GridBagConstraints.RELATIVE;

53addComponent( buttons[ 1 ] );

54

55// buttons[2] -- weightx and weighty are 1: fill is BOTH

56constraints.gridwidth = GridBagConstraints.REMAINDER;

57addComponent( buttons[ 2 ] );

58

59// comboBox -- weightx is 1: fill is BOTH

60constraints.weighty = 0;

61constraints.gridwidth = GridBagConstraints.REMAINDER;

62addComponent( comboBox );

63

64// buttons[3] -- weightx is 1: fill is BOTH

65constraints.weighty = 1;

66constraints.gridwidth = GridBagConstraints.REMAINDER;

67addComponent( buttons[ 3 ] );

68

69// buttons[4] -- weightx and weighty are 1: fill is BOTH

70constraints.gridwidth = GridBagConstraints.RELATIVE;

71 addComponent( buttons[ 4 ] );

72

73// list -- weightx and weighty are 1: fill is BOTH

74constraints.gridwidth = GridBagConstraints.REMAINDER;

75addComponent( list );

76} // end GridBagFrame2 constructor

77

78// add a component to the container

79private void addComponent( Component component )

80{

81layout.setConstraints( component, constraints );

82add( component ); // add component

83} // end method addComponent

84} // end class GridBagFrame2

Figure 22.24. Test class for GridBagDemo2.

(This item is displayed on page 1045 in the print version)

1// Fig. 22.24: GridBagDemo2.java

2// Demonstrating GridBagLayout constants.

3import javax.swing.JFrame;

4

5public class GridBagDemo2

6{

7public static void main( String args[] )

8{

9GridBagFrame2 gridBagFrame = new GridBagFrame2();

10gridBagFrame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );

11gridBagFrame.setSize( 300, 200 ); // set frame size

12gridBagFrame.setVisible( true ); // display frame

13} // end main

14} // end class GridBagDemo2

JButton buttons[ 2 ] (lines 5657) has weightx and weighty values of 1. The fill variable is BOTH. This

JButton is the last component on the line, so REMAINDER is used. The JButton is added to the content pane with a call to addComponent.

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The JComboBox (lines 6062) has a weightx of 1 and a weighty of 0. The JComboBox will not grow in the vertical direction. The JComboBox is the only component on the line, so REMAINDER is used. The JComboBox is added to the content pane with a call to addComponent.

JButton buttons[ 3 ] (lines 6567) has weightx and weighty values of 1. The fill variable is BOTH. This JButton is the only component on the line, so REMAINDER is used. The JButton is added to the content pane with a call to addComponent.

JButton buttons[ 4 ] (lines 7071) has weightx and weighty values of 1. The fill variable is BOTH. This JButton is the next-to-last component on the line, so RELATIVE is used. The JButton is added to the content pane with a call to addComponent.

The JList (lines 7475) has weightx and weighty values of 1. The fill variable is BOTH. The JList is added to the content pane with a call to addComponent.

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22.10. Wrap-Up

This chapter completes our introduction to GUI. In this chapter, you learned about more advanced GUI topics, such as menus, sliders, pop-up menus and the multiple-document interface. All these components can be added to existing applications to make them easier to use and understand. In the next chapter, you will learn about multithreading, a powerful capability that allows applications to use threads to perform multiple tasks at once.

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Summary

JSliders enable the user to select from a range of integer values. JSliders can display major

tick marks, minor tick marks and labels for the tick marks. They also support snap-to ticks, where positioning the thumb between two tick marks causes the thumb to snap to the closest tick mark.

If a JSlider has the focus, the left and right arrow keys cause the thumb of the JSlider to

decrease or increase by 1. The down and up arrow keys also cause the thumb of the JSlider to decrease or increase by 1, respectively. The PgDn (page down) key and PgUp (page up) key cause the thumb of the JSlider to decrease or increase by block increments of one-tenth of the range of values, respectively. The Home key moves the thumb to the minimum value of the JSlider, and the End key moves it to the maximum value.

JSliders have either horizontal or vertical orientation. For a horizontal JSlider, the minimum

value is at the extreme left and the maximum value is at the extreme right. For a vertical JSlider, the minimum value is at the extreme bottom and the maximum value is at the extreme top. The position of the thumb indicates the current value of the JSlider. Method getValue of class JSlider returns the current thumb position.

Method setMajorTickSpacing of class JSlider sets the spacing for tick marks on a JSlider. Method setPaintTicks with a TRue argument indicates that the tick marks should be displayed.

JSliders generate ChangeEvents when the user interacts with a JSlider. A ChangeListener declares method stateChanged that can respond to ChangeEvents.

Every window generates window events when the user manipulates it. Interface WindowListener provides seven window-event-handling methodswindowActivated, windowClosed, windowClosing, windowDeactivated, windowDeiconified, windowIconified and windowOpened.

Menus are an integral part of GUIs. Menus allow the user to perform actions without

unnecessarily cluttering a graphical user interface with extra GUI components. In Swing GUIs, menus can be attached only to objects of classes with method setJMenuBar (e.g., JFrame and

JApplet).

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The classes used to declare menus are JMenuBar, JMenuItem, JMenu, JCheckBoxMenuItem and JRadioButtonMenuItem.

A JMenuBar is a container for menus. A JMenuItem is a GUI component inside a menu that, when

selected, causes an action to be performed. A JMenu contains menu items and can be added to a JMenuBar or to other JMenus as submenus.

When a menu is clicked, it expands to show its list of menu items. JMenu method addSeparator adds a separator line to a menu.

When a JCheckBoxMenuItem is selected, a check appears to the left of the menu item. When the JCheckBoxMenuItem is selected again, the check is removed.

When multiple JRadioButtonMenuItems are maintained as part of a ButtonGroup, only one item

in the group can be selected at a given time. When an item is selected, a filled circle appears to its left. When another JRadioButtonMenuItem is selected, the filled circle to the left of the previously selected item is removed.

AbstractButton method setMnemonic specifies the mnemonic for an AbstractButton. Mnemonic

characters are normally displayed with an underline.

A modal dialog box does not allow access to any other window in the application until the dialog

is dismissed. The dialogs displayed with class JOptionPane are modal dialogs. Class JDialog can be used to create your own modal or nonmodal dialogs.

Context-sensitive pop-up menus are created with class JPopupMenu. On most systems, the

popup trigger event occurs when the user presses and releases the right mouse button. MouseEvent method isPopupTrigger returns TRue if the pop-up trigger event occurred.

JPopupMenu method show displays a JPopupMenu. The first argument specifies the origin

component, which helps determine where the JPopupMenu will appear. The last two arguments are the coordinates from the origin component's upper-left corner, at which the JPopupMenu appears.

Class UIManager contains nested class LookAndFeelInfo that maintains information about a look- and-feel.

UIManager static method getInstalledLookAndFeels gets an array of

UIManager.LookAndFeelInfo objects that describe the available look-and-feels.

UIManager static method setLookAndFeel changes the look-and-feel. SwingUtilities static

method updateComponentTreeUI changes the look-and-feel of every component attached to its Component argument to the new look-and-feel.

Many of today's applications use a multiple-document interface (MDI) to manage several open

documents that are being processed in parallel. Swing's JDesktopPane and JInternalFrame classes provide support for creating multiple-document interfaces.

A JTabbedPane arranges GUI components into layers in which only one layer is visible at a time.

Users access each layer via a tab similar to those on folders in a file cabinet. When the user clicks a tab, the appropriate layer is displayed.

BoxLayout is a layout manager that allows GUI components to be arranged left-to-right or top- to-bottom in a container.

Class Box declares a container with BoxLayout as its default layout manager and provides static methods to create a Box with a horizontal or vertical BoxLayout.

GridBagLayout is a layout manager similar to GridLayout. It differs in that each component size can vary, and components can be added in any order.

A GridBagConstraints object specifies how a component is placed in a GridBagLayout. Method

setConstraints of class GridBagLayout takes a Component argument and a GridBagConstraints argument and sets the constraints of the Component.

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Terminology

add method of class JMenuBar

addWindowListener method of class Window

anchor field of class GridBagConstraints border

BOTH constant of class GridBagConstraints

Box class

BoxLayout class

CENTER constant of class GridBagConstraints ChangeEvent class

ChangeListener interface child window

context-sensitive pop-up menu createGlue method of class Box createHorizontalBox method of class Box

createHorizontalGlue method of class Box createHorizontalStrut method of class Box createRigidArea method of class Box createVerticalBox method of class Box createVerticalGlue method of class Box createVerticalStrut method of class Box

Dimension class

dispose method of class Window document

EAST constant of class GridBagConstraints getClassName method of class

UIManager.LookAndFeelInfo

getInstalledLookAndFeels method of class UIManager getPreferredSize method of class Component getSelectedText method of class

JTextComponent

getValue method of class JSlider GridBagConstraints class

GridBagLayout class

gridheight field of class GridBagConstraints gridwidth field of class GridBagConstraints gridx field of class GridBagConstraints gridy field of class GridBagConstraints HORIZONTAL constant of GridBagConstraints horizontal glue

isPopupTrigger method of class MouseEvent isSelected method of class AbstractButton JCheckBoxMenuItem class

JDesktopPane class

JDialog class

JFrame class

JInternalFrame class

JMenu class

JMenuBar class

JMenuItem class

JRadioButtonMenuItem class

JSlider class

JTabbedPane class

line wrapping

LookAndFeelInfo nested class of class UIManager

menu

menu bar menu item

metal look-and-feel

minor tick marks of JSlider mnemonic

modal dialog box

multiple document interface (MDI)

NONE constant of class GridBagConstraints NORTH constant of class GridBagConstraints NORTHEAST constant of class GridBagConstraints NORTHWEST constant of class GridBagConstraints opaque

origin component

pack method of class Window paintComponent method of class JComponent parent window

parent window for a dialog box pluggable look and feel (PLAF) pop-up trigger event

RELATIVE constant of class GridBagConstraints REMAINDER constant of class GridBagConstraints rigid area

scrollbar policies selected text

separator line in a menu

setConstraints method of class GridBagLayout setDefaultCloseOperation method of class JFrame setInverted method of class JSlider

setJMenuBar method of class JFrame setLocation method of class Component