Java Reference
In-Depth Information
Table 10.1 Definitions of Component Groups
Group
Definition
Virtual machine (VM)
CLDC Configuration VM; the bytecode engine written
in native code (Note: Java Configuration classes are not
included.)
MIDP layer
MIDP implementation only (Note: the underlying Con-
figuration and VM are not included.)
MIDP/CLDC run-time environment
Combination of the MIDP layer, Configuration classes
and VM, as seen from the point of view of the Symbian
OS architecture (Note: the AMS is not included.)
Java ME subsystem
Combination of the AMS and the Java ME run-time
environment, as seen from the point of view of the
Symbian OS architecture
Java ME platform
AMS and the Java ME run-time environment, as seen
from the point of view of a hosted Java application
Java ME run-time environment
MIDP/CLDC environment, as seen from the point of
view of a hosted Java application (Note: the AMS is not
included)
group definition, although it is relevant to it, we explicitly note that it is
excluded from that group definition.
Now let's take a first look at Figure 10.3, which depicts the two
main processes in the Java ME subsystem implementation on Symbian
OS. There are two main process types: the AMS runs in a single native
process and takes care of the lifecycle and resource management of
MIDlets amongst many other responsibilities; each MIDlet suite executes
in the MIDP/CLDC run-time environment which runs in a separate native
process.
MIDlet 1
1
n
MIDP/CLDC
process
AMS process
MIDlet n
Figure 10.3 Interaction between the AMS and the MIDP/CLDC run-time processes
When the user wishes to launch a MIDlet, the AMS spawns a new child
process executing the MIDP/CLDC run-time environment, for each appli-
cation suite. That is, a new run-time process is spawned only for the first
MIDlet that is launched from the suite. Additional concurrently running
MIDlets from the same suite are executed in the same run-time process.
The interaction between the AMS and the MIDP/CLDC run-time
process is not one way. There are a few cases which require the AMS to
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