Sun Microsystems 2 manual Other Multitasking Issues, Switching the Foreground MIDlet

C H A P T E R 4

Other Multitasking Issues

Multitasking raises some issues related to the behavior of the Java Wireless Client software. This chapter describes the issues, how they are handled by the Java Wireless Client software, and possible alternatives.

Most of the issues discussed in this chapter relate to the implementation of the Java platform AMS. The same issues must be addressed by the Native AMS.

Switching the Foreground MIDlet

In a system that cannot run concurrent MIDlets, each MIDlet effectively runs alone and it potentially has access to all the resources available on the system. The entire runtime environment is shut down when the MIDlet exits. Multitasking environments work differently.

With multitasking, a MIDlet is not alone on the system. The MIDlet runs in its own environment (its task), but at most one MIDlet can have access to the device’s display and to the device’s input mechanisms, such as keypad and pointer events. No MIDlets have access to the device’s display and input mechanisms if the user is interacting with a native application. Managing which MIDlet has access to the device display and input mechanisms necessitated the introduction of the foreground and background states:

■A foreground MIDlet can draw on the screen and receive keystrokes (and pointer events, if the device has pointer input).

■A background MIDlet cannot draw to the device display, and the system ignores any graphics operations it emits. A background MIDlet cannot receive any keypad or pointer events.

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