Persistent Storage I: MIDP Record Store - Beginning J2ME: From Novice to Professional - page 101

CHAPTER 8
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Persistent Storage I:
MIDP Record Store
M IDP applications have to run seamlessly on many devices. You've already seen how this
can be a challenge in the user interface arena. The trick there was to use abstract concepts that
would be mapped to the screen by a device-specific implementation.
MIDP's approach to persistent storage is basically the same. Your application could run on
a device with flash ROM or battery-backed RAM. MIDP applications don't really care; all they
know about are small databases called record stores. It's up to the device's MIDP implementa-
tion to map record stores in some reasonable manner to whatever persistent storage is available.
These are small amounts of data we're talking about; the MIDP specification dictates that
the minimum amount of persistent storage is only 8KB. The record store mechanism is highly
effective for these small amounts of persistent storage.
Overview
In MIDP, persistent storage is centered around record stores. A record store is a small database
that contains pieces of data called records . Record stores are represented by instances of
javax.microedition.rms.RecordStore . The scope of a record store can either be limited to a
single MIDlet suite or be shared between MIDlet suites. Said another way, you can either
restrict a MIDlet to only access record stores that were created by a MIDlet in the same suite,
or you can explicitly allow MIDlets from multiple suites to share a record store . Figure 8-1
shows the relationship between MIDlet suites and record stores.
Record stores are identified by a name. Within a MIDlet suite's record stores, the names
must be unique.
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