Handling Events - Beginning Java - page 949

use this to create buttons for any of the Action objects that you created for the menus, and have the toolbar
button events taken care of without any further work.
For example, you could add a button you create from the openAction object corresponding to the Open
menu item in the File menu with the following statements:
JButton button = new JButton(openAction); // Create button from Action
toolBar.add(button); // Add a toolbar button
That's all you need basically. The JButton constructor creates a JButton object based on the Action
object that you pass as the argument. The properties defined in the Action object apply to the button, so this
matches the Open menu item in the File menu. More than that, because the button and the menu item share
a single Action object, clicking on either the menu item or the toolbar button calls the same actionPer-
formed() method, which is the one you have defined for the Action object. The add() method for toolBar
adds the JButton object to the toolbar.
A nice feature of a JToolBar object is that it can highlight the button that the mouse cursor is over with
a mechanism that is referred to as rollover action . To switch on this feature you can call setRollover() for
the JToolBar object with the argument as true :
toolBar.setRollover(true);
Add this statement to the SketcherFrame constructor, immediately before you add the toolbar to the con-
tent pane. Calling the setRollover() method with false as the argument switches off rollover action. You
will see button highlighting in operation in Sketcher.
Inhibiting Text on a Toolbar Button
Because a toolbar button is created using the Action object properties that you have defined for the corres-
ponding menu item, it has a NAME value, and the text for the name displays on the toolbar button by default.
This is not want you want in most cases. You can prevent the name from being displayed by calling the
setHideActionText() for a JButton toolbar button with an argument value true :
button.setHideActionText(true);
Calling this method with a false argument would cause the text to be displayed, so you can switch the text
on and off. What you really want, though, is to be able to display an icon on a toolbar button instead of
displaying the text.
Adding Icons to Toolbar Buttons
A reference to an icon is generally stored in a variable of type javax.swing.Icon , which is an interface
that declares methods that return the height and width of an icon in pixels — getHeight() and getWidth()
methods, respectively. The Icon interface also declares the paint() method that paints the icon image on
a component. The javax.swing.ImageIcon class implements the Icon interface and you use this class to
create an icon object in your program from a file that contains the data defining the icon image.
The ImageIcon class has several constructors, and the one you use accepts a String argument that spe-
cifies the path for the file in which the icon image is found. The String object that you pass as the argument
can be just the file name, in which case the file should be in the current directory when Sketcher executes.
You can also supply a string that specifies the full path to the file containing the image. I'm putting the files