Swing I - Java - page 934

can be used with any JButton or JMenuItem to change the action command for that
component. Among other things, this will allow you to have different action com-
mands for two buttons, two menu items, or a button and menu item even though
they have the same string written on them.
The method setActionCommand takes a String argument that becomes the new action
command for the calling button or menu item. For example, consider the following code:

setAction-
Command

JButton nextButton = new JButton("Next");
nextButton.setActionCommand("Next Button");
JMenuItem chooseNext = new JMenuItem("Next");
chooseNext.setActionCommand("Next Menu Item");

If we had not used setActionCommand in the preceding code, then the button nextButton
and the menu item chooseNext would both have the action command "Next" and so we
would have no way to tell which of the two components nextButton and chooseNext an
action event "Next" came from. However, using the method setActionCommand , we can
give them the different action commands "Next Button" and "Next Menu Item" .
The action command for a JButton or JMenuItem is kept as the value of a private
instance variable for the JButton or JMenuItem . The method setActionCommand is
simply an ordinary mutator method that changes the value of this instance variable.

setActionCommand and getActionCommand
Every button and every menu item has a string associated with it that is known as the action
command for that button or menu item. When the button or menu item is clicked, it fires an
action event e . The following invocation returns the action command for the button or menu
item that fired e :

e.getActionCommand()

The method actionPerformed typically uses this action command string to decide which
button or menu item was clicked.
The default action command for a button or menu item is the string written on it, but if you
want, you can change the action command with an invocation of the method setAction-
Command . For example, the menu item chooseNext created by the following code will display
the string "Next" when it is a menu choice, but will have the string "Next Menu Item" as its
action command.
EXAMPLE
JMenuItem chooseNext = new JMenuItem("Next");
chooseNext.setActionCommand("Next Menu Item");

An alternate approach to defining action listeners is given in the next subsection.
That technique is, among other things, another way to deal with multiple buttons or
menu items that have the same thing written on them.