g.setColor(Color.DARK GRAY); g.fillRect(0,0,30,30); g.setColor(c);

g.fill3DRect(3, 3, 24, 24, false); g.dispose();

Icon selectedIcon = new ImageIcon(image);

/* Create and configure the button. */

JRadioButton button = new JRadioButton(unselectedIcon); button.setSelectedIcon(selectedIcon); button.addActionListener( new ActionListener() {

public void actionPerformed(ActionEvent e) {

//The action for this button sets the current drawing color

//in the display to c.

display.setCurrentColor(c);

}

});

grp.add(button); if (selected)

button.setSelected(true);

return button;

} // end makeColorRadioButton

It is possible to create radio buttons and check boxes from Actions. The button takes its name, main icon, tooltip text, and enabled/disabled state from the action. However, in Java 5.0, an action has no property corresponding to the selected/unselected state. This means that you can’t check or set the selection state through the action. In Java 6.0, the action API is considerably improved, and among the changes is support for selection state.

12.3.4Toolbars

It has become increasingly common for programs to have a row of small buttons along the top or side of the program window that o er access to some of the commonly used features of the program. The row of buttons is known as a tool bar . Typically, the buttons in a tool bar are presented as small icons, with no text. Tool bars can also contain other components, such as

JTextFields and JLabels.

In Swing, tool bars are represented by the class JToolBar. A JToolBar is a container that can hold other components. It is also itself a component, and so can be added to other containers. In general, the parent component of the tool bar should use a BorderLayout. The tool bar should occupy one of the edge positions—NORTH, SOUTH, EAST, or WEST—in the BorderLayout. Furthermore, the other three edge positions should be empty. The reason for this is that it might be possible (depending on the platform and configuration) for the user to drag the tool bar from one edge position in the parent container to another. It might even be possible for the user to drag the toolbar o its parent entirely, so that it becomes a separate window.

Here is a picture of a tool bar from the sample program ToolBarDemo.java.

equivalent CONTROL-S, and the “Undo” command corresponds to CONTROL-Z. (Under Mac OS, the keyboard equivalents for these commands would probably be META-C and META-Z, where META refers to holding down the “apple” key.) The keyboard equivalents for menu commands are referred to as accelerators.

The class javax.swing.KeyStroke is used to represent key strokes that the user can type on the keyboard. A key stroke consists of pressing a key, possibly while holding down one or more of the modifier keys control, shift, alt, and meta. The KeyStroke class has a static method, getKeyStroke(String), that makes it easy to create key stroke objects. For example,

KeyStroke.getKeyStroke( "ctrl S" )

returns a KeyStroke that represents the action of pressing the “S” key while holding down the control key. In addition to “ctrl”, you can use the modifiers “shift”, “alt”, and “meta” in the string that describes the key stroke. You can even combine several modifiers, so that

KeyStroke.getKeyStroke( "ctrl shift Z" )

represents the action of pressing the “Z” key while holding down both the control and the shift keys. When the key stroke involves pressing a character key, the character must appear in the string in upper case form. You can also have key strokes that correspond to non-character keys. The number keys can be referred to as “1”, “2”, etc., while certain special keys have names such as “F1”, “ENTER”, and “LEFT” (for the left arrow key). The class KeyEvent defines many constants such as VK ENTER, VK LEFT, and VK S. The names that are used for keys in the keystroke description are just these constants with the leading “VK ” removed.

There are at least two ways to associate a keyboard accelerator with a menu item. One is to use the setAccelerator() method of the menu item object:

JMenuItem saveCommand = new JMenuItem( "Save..." ); saveCommand.setAccelerator( KeyStroke.getKeyStroke("ctrl S") );

The other technique can be used if the menu item is created from an Action. The action property Action.ACCELERATOR KEY can be used to associate a KeyStroke with an Action. When a menu item is created from the action, the keyboard accelerator for the menu item is taken from the value of this property. For example, if redoAction is an Action representing a “Redo” action, then you might say:

redoAction.putValue( Action.ACCELERATOR KEY, KeyStroke.getKeyStroke("ctrl shift Z") );

JMenuItem redoCommand = new JMenuItem( redoAction );

or, alternatively, you could simply add the action to a JMenu, editMenu, with editMenu.add(redoAction). (Note, by the way, that accelerators apply only to menu items, not to push buttons. When you create a JButton from an action, the ACCELERATOR KEY property of the action is ignored.)

Note that you can use accelerators for JCheckBoxMenuItems and JRadioButtonMenuItems, as well as for simple JMenuItems.

For an example of using keyboard accelerators, see the solution to Exercise 12.2.

By the way, as noted above, in the Macintosh operating system, the meta (or apple) key is usually used for keyboard accelerators instead of the control key. If you would like to make your program more Mac-friendly, you can test whether your program is running under Mac OS and, if so, adapt your accelerators to the Mac OS style. The recommended way to detect Mac

OS is to test the value of System.getProperty("mrj.version"). This function call happens to return a non-null value under Mac OS but returns null under other operating systems. For example, here is a simple utility routine for making Mac-friendly accelerators:

/**

*Create a KeyStroke that uses the meta key on Mac OS and

*the control key on other operating systems.

*@param description a string that describes the keystroke,

*without the "meta" or "ctrl"; for example, "S" or

*"shift Z" or "alt F1"

*@return a keystroke created from the description string

*with either "ctrl " or "meta " prepended

*/

private static KeyStroke makeAccelerator(String description) { String commandKey;

if ( System.getProperty("mrj.version") == null ) commandKey = "ctrl";

else

commandKey = "meta";

return KeyStroke.getKeyStroke( commandKey + " " + description );

}

12.3.6HTML on Buttons

As a final stop in this brief tour of ways to spi up your buttons, I’ll mention the fact that the text that is displayed on a button can be specified in HTML format. HTML is the markup language that is used to write web pages. A brief introduction to HTML can be found in Subsection 6.2.3. HTML allows you to apply color or italics or other styles to just part of the text on your buttons. It also makes it possible to have buttons that display multiple lines of text. (You can also use HTML on JLabels, which can be even more useful.) Here’s a picture of a button with HTML text (along with a “Java” icon):

If the string of text that is applied to a button starts with “<html>”, then the string is interpreted as HTML. The string does not have to use strict HTML format; for example, you don’t need a closing </html> at the end of the string. To get multi-line text, use <br> in the string to represent line breaks. If you would like the lines of text to be center justified, include the entire text (except for the <html>) between <center> and </center>. For example,

JButton button = new JButton(

"<html><center>This button has<br>two lines of text</center>" );

creates a button that displays two centered lines of text. You can apply italics to part of the string by enclosing that part between <i> and </i>. Similarly, use <b>...</b> for bold text and <u>...</u> for underlined text. For green text, enclose the text between <font color=green> and </font >. You can, of course, use other colors in place of “green.” The “Java” button that is shown above was created using: