Embedded Java - JavaTech: An Introduction to Scientific and Technical Computing with Java - page 652

We then review a selection of Java hardware processors, most of which execute
bytecode instructions directly rather than interpret them with a JVM. Some Java
processors can run standalone while others act as co-processors to assist primary
processors with Java programs. We look at a selection of Java board systems that
include a Java microprocessor and various supporting hardware such as memory
and power regulation. One type of Java board is designed like a memory module
that plugs into the expansion slot of a carrier board. The carrier boards in turn
provide the physical hardware for serial I/O ports, Ethernet connectors, ADCs
(Analog to Digital Converters) for measuring analog inputs, etc.
We give an example program that illustrates how to program a Java card to
communicate over a serial line to the Java program discussed in Chapter 23. Some
of the Java boards can provide for embedded servers that connect a system to the
network and allow for control and monitoring of that system by remote clients. We
discussed custom servers in Chapters 14 and 15 and in a second example program
we adapt such a server to a Java processor intended for embedded applications.
24.2 Embedded Java for science and engineering
Applications of embedded Java in science and engineering can take advantage
of the same language features as do commercial consumer devices. For example,
adding Java networking to remote devices, such as process equipment in a man-
ufacturing plant or sensors in an experiment, increases the options for control,
monitoring, diagnostics, calibration, and data gathering. In Part II we showed how
youbuild custom tiny web servers and client/server systems with Java. Adding
such servers to lots of small devices that make up a large system greatly expands
the depth and granularity in the control and monitoring of such a system.
24.3 J2ME - Java 2 Micro Edition
The Java 2 Standard Edition (J2SE) aims for today's typical desktop platform,
which should easily possess sufficient memory and processing speed to handle the
demands of most programs built with it. Developers can have high confidence that
if their programs run on one system with the J2SE it will run on all of them. Small
computer platforms and embedded systems, however, involve environments with
an enormous diversity in performance capabilities and memory resources. No
single group of Java classes could do justice to systems that range from a Java
Card [1] with a few kilobytes of memory to a high-end PDA with many megabytes.
As discussed in Chapter 1, the initial attempt by Sun to match Java to differ-
ent micro platforms resulted in the JavaCard , EmbeddedJava , and PersonalJava
frameworks based on Java 1.1 classes. With Java 2 came the decision to replace
EmbeddedJava and PersonalJava with a more systematic scheme called Java 2
Micro Edition or J2ME [2]. J2ME does not encompass a single set of classes as do
J2SE and J2EE, but instead it allows for subsets of classes called configurations .