The CLDC

The Connected Limited Device Configuration, or CLDC for short, is the first of two configurations defined by the Java 2 Micro Edition (J2ME) standards process. A configuration defines a complete Java runtime environment, including the capabilities of the Java virtual machine (VM) and the core set of Java runtime libraries that are available to applications. As such, configurations are the basic blocks of J2ME. For more details, see the articles J2ME Core Concepts and Understanding the CLDC.

CLDC Versions

There are two versions of the CLDC currently defined. The first, version 1.0, is defined by JSR-30: J2ME Connected, Limited Device Configuration. The second, version 1.1, is defined by JSR-139: Connected Limited Device Configuration 1.1. (Notice how the comma in the full name of the configuration was dropped — in practice, nobody ever used the comma since it made for confusing sentences.)

What's different between versions 1.0 and 1.1? Version 1.1 basically adds J2SE features that were left out of version 1.0: floating-point support, weak references, an error class (NoClassDefFoundError), and various small changes. The floating-point support is the biggest change from an application development standpoint. The full list of new and changed functionality is found in the CLDC 1.1 specification.

CLDC Resources

The CLDC specifications are available for download from the Java Community Process (JCP) website using the links above. If you're a J2ME programmer, you should read both specifications in order to understand what you can and cannot do in a CLDC environment.

You can download reference implementations of the CLDC from Sun's main CLDC page, which also has links to the JCP pages that define the CLDC. Unless you're interested in porting the CLDC to a new platform, though, you'll probably want to download a MIDP implementation instead, since it will also include a CLDC implementation. By itself, the CLDC is not that useful — it defines too simple an environment.