Java 2 Micro Edition Overview - Java 2 Micro Edition Application Development - page 7

Configurations
Currently, just two configurations—CLDC and CDC—exist. The CDC profiles are still in the
specification process, but the CLDC is finished and forms the basis for MIDP and PDAP.
The CLDC was designed especially for the mobile phone and PDA class of devices. It requires
128 to 512KB of memory (RAM and ROM), a battery power supply, and a network connection of
at least 9600bps.
The CLDC API contains simplified versions of java.lang , java.io , java.util , and the
new package javax.microedition.io , described in more detail in Chapter 6 , "Networking:
The Generic Connection Framework."
Because CLDC was specified for processors that may not provide floating-point support, float
and double are not supported. However, CLDC 1.1, the next generation of the CLDC profile,
adds support for floating point operations. Support for Java Native Interfaces (JNI) also is not
included in CLDC. The reflection API is very limited; for example, user-defined class loaders are
not available. Finalization is not supported.
Another restriction is that class files need to be preverified before execution with the KVM. The
preverification step inserts hints into the class files that simplify and speed up the actual
verification of the classes on the device. The preverification step includes a check for invalid data
types, so class files containing float s will be rejected in this step for the original CLDC profile.
The second configuration available, CDC, targets more powerful devices like set top boxes, video
phones, and gaming consoles with at least 512KB ROM and 256KB RAM as well as a fast
network connection.
Profiles
In contrast to the configurations, which are independent of the device's purpose, the profiles cover
aspects that are specific to a certain device type. For example, the profiles cover the user interface
and persistent data storage. Currently, two profiles are available: MIDP and PDAP.
The Mobile Information Device Profile (MIDP)
MIDP targets cellular phones and simple pagers. It provides a very simple and abstract user
interface built of simple elements. The user interface is divided into a high-level and a low-level
API. The high-level API provides simple elements such as lists and forms, but it offers only very
limited control over the concrete appearance on the screen. The low-level API provides full
control over the screen, but no widgets; it's mainly intended for games. The UI API is not
compatible with any other Java UI API, such as AWT or SWING.
The Personal Digital Assistant Profile (PDAP)
Just as the name suggests, PDAP targets PDAs. It provides a user interface that is a subset of the
AWT package of the Java 2 Standard Edition and access to the Personal Information Management
databases of the device. In contrast to MIDP, PDAP is based on the newer CLDC-NG
configuration because the AWT classes require floating point support. In order to access existing
MIDP applications, the PDA profile is a complete superset of the MID Profile. Thus, any MIDP
application can run on devices supporting PDAP. However, in contrast to MIDP devices, which
have always a wireless connection, existing PDAs don't necessarily provide permanent network
access.