Java Reference
In-Depth Information
If you are interested in eventually taking the exam to become a Sun Certified
Java Programmer, you need to become familiar with the J2SE.
J2ME
J2ME is not a slimmed-down version of J2SE. Instead, it establishes a proce-
dure for defining what a particular JVM designed for an electronic device will
provide. The J2ME technology has two components:
Configurations.
Define the type of JVM that is being targeted.
Profiles.
Describe specification details about the device that is being tar-
geted. Each device has a profile listing the standard Java APIs available
for that device.
Configurations are composed of Java APIs and virtual machines designed to
run on two different types of devices. The first type of device is those with
128-512K of memory. This configuration is called the Connected Limited
Device Configuration (CLDC), and the corresponding JVM is referred to as the
K Virtual Machine, or KVM.
The second configuration is for devices with more than 512K of memory.
This configuration is called the Connected Device Configuration and uses the
standard JVM, with all the same capabilities of a regular desktop computer.
Profiles are defined by the Java Community Process (JCP), which allows for
input from any industry interested in a profile for a particular type of elec-
tronic device. For example, a profile would be created for wireless phones,
with the profile defining the configuration to use for wireless phones and the
Java APIs that will be available. Any company that had an interest in wireless
phones could join the Java Community Process to help determine which con-
figuration to choose and what the Java API would look like for developing
Java applications for wireless phones.
J2EE
J2EE is a collection of Java technologies that create a platform for distributed
applications. Along with the J2SE (some of the J2EE technologies are actually a
part of the Java 2, Standard Edition), J2EE allows for the most complex of mul-
titier software applications to be portable across multiple platforms.
J2EE consists of the following technologies:
Enterprise JavaBeans (EJB).
An EJB is a component architecture for the
development and deployment of object-oriented distributed business
applications. Applications written using the EJB architecture are scal-
able, transactional, and multiuser secure.
Java Servlets.
A servlet is a Java application that runs in a Web server.
