The Connected Limited Device Configuration - Java 2 Micro Edition Application Development - page 24

Chapter 2. The Connected Limited Device
Configuration
IN THIS CHAPTER
• General CLDC Limitations
• CLDC Application Design
• CLDC APIs
• CLDC Profiles
• Java Application Deployment
• JAM on MIDP
• JAM for PDAP
This chapter describes the general concepts and limitations of the Connected Limited Device
Configuration (CLDC). You already saw some of the limitations in Chapter 1 , "Java 2 Micro
Edition Overview." Here, you'll see a complete list, and also take a closer look at the API
packages available in the CLDC. This chapter also discusses the packages and classes of the
Mobile Information Device (MID) and Personal Digital Assistant (PDA) profiles including
extensions of CLDC classes. Finally, it describes the special steps involved in J2ME application
deployment.
General CLDC Limitations
In order to make the Java feature set suitable for very limited devices such as cellular phones or
PDAs, CLDC's developers had to limit the feature set in several ways. This section first describes
the general language and virtual machine limitations and some consequences of the missing
reflection capabilities. It then discusses the simplified security and highlights some general
limitations resulting directly from the limited hardware capabilities of CLDC devices.
General Java Language Limitations
For CLDC, the Java language itself was simplified slightly. The following restrictions hold for the
Java language in CLDC:
• No floating-point support (CLDC 1.0 only)
• No reflection
• No thread groups and daemon threads
• No weak references (CLDC 1.0 only)
• Error handling may be limited
• No finalization; CLDC does not support the finalize() method
• No Java Native Interface (JNI)
• No user-defined class loaders
The missing floating-point support is perhaps the most significant limitation because it makes
development of calculation or spreadsheet programs very difficult. The MathFP API from Onno
Honnes ( www.jscience.net ) provides fixed-point calculations as a substitute, but fixed-point
arithmetic is not a complete replacement for floating-point support.
CLDC supports full exception handling, but limitations may apply to the Error exception classes.
The problem is that it is very difficult to handle errors like those that arise from heap exceptions,