Sun Microsystems Computer Accessories manual Assigning Abstract Commands to Buttons

There are two ways you can do a button press at the same time as pressing Shift or Alt:

■Map the buttons to the keyboard, as in the previous section, and press the key associated with the button at the same time as the Shift or Alt keys

■Press the button Shift-Lock or Alt-Lock and then do the button press. Press Shift-Lock or Alt-Lock again to revert to the initial state.

For example:

keyboard.handler.qwerty.A = 'a' 'A' '?'

Assigning Abstract Commands to Buttons

Abstract commands are provided in the MIDP specification in order to allow an application to issue a screen command without having to take into account how the user selects that command on a specific device—making the application more portable. The idea is to separate the semantics of the command from its execution on the device. The semantics are defined in the application and the execution is defined in the implementation of MIDP on the specific device.

The semantics of an abstract command include:

■Label—the command name for display purposes

■Type—the category of the command, for example BACK or HELP. The command type is used to help determine how a command is mapped onto a device

■Priority—a priority number. The command priority is used to help determine how a command is mapped onto a device.

In the MIDP Reference Implementation, which underlies the J2ME Wireless Toolkit, there is an implicit order of precedence among the command types. This command precedence also impacts on the assignment of a command to a preferred button. If two commands of different types are vying for the same button, the command whose type has higher precedence prevails.

TABLE 3 shows the abstract command types in order of precedence in the J2ME Wireless Toolkit and the MIDP Reference Implementation:

TABLE 3 Abstract Command Types in Order of Precedence

Command Type	Description
BACK	Returns the user to the logically previous screen
EXIT	Exits from the application
CANCEL	Standard negative answer to a dialog implemented by the
	current screen
STOP	Stop some currently running process or operation

Chapter 3 Examining Device Property Files 33