CLDC 8

Goals, Requirements and Scope

Goals

The goal of the CLDC Specification is to standardize a highly portable, minimum-footprint Java™ application development platform for resource-constrained, connected devices.

The devices targeted by the CLDC Specification have the following general characteristics:

Cell phones, two-way pagers, sensors, wireless modules, IoT and M2M platforms, home appliances, low-end TV set-top boxes, and point of sale terminals are some, but not all, of the devices that might be supported by this specification.

More specifically, the CLDC Specification defines a Java application development platform with the following characteristics and goals:

Hardware Requirements

CLDC is intended to run on a wide variety of small devices. The underlying hardware capabilities of these devices vary considerably, and therefore the CLDC Specification does not impose any specific hardware requirements other than memory requirements. Even for memory limits, the CLDC Specification defines only minimum limits. The actual CLDC target devices may have significantly more memory than the minimum.

The Specification recommends that:

The ratio of volatile to non-volatile memory in the total memory budget can vary considerably depending on the target device and the role of the Java platform in the device. If the Java platform is used strictly for running system applications that are built in a device, then applications can be pre-linked and preloaded, and a very limited amount of volatile memory is needed. If the Java platform is used for running dynamically downloaded content, then devices will need a higher ratio of volatile memory.

Software Requirements

Like the hardware capabilities, the system software in CLDC target devices varies considerably. For instance, some of the devices may have a full-featured operating system that supports multiple, concurrent operating system processes and a hierarchical file system. Many other devices may have extremely limited system software with a minimal file system. Faced with such variety, CLDC makes minimal assumptions about the underlying system software.

Generally, the CLDC Specification assumes that a minimal host operating system or kernel is available to manage the underlying hardware. This host operating system must provide at least one schedulable entity to run the Java Virtual Machine. The host operating system does not need to support separate address spaces or processes, nor does it have to make any guarantees about the real-time scheduling or latency behavior.

Unsupported Java SE 8 features (informative)

Due to the constraints of the target devices, there are various Java SE 8 features, that are not available on CLDC 8. These include:

1. The term non-volatile is used to indicate that the memory is expected to retain its contents between the user turning the device "on" or "off". For the purposes of the CLDC Specification, it is assumed that non-volatile memory is usually accessed in read mode, and that special setup may be required to write to it. Examples of non-volatile memory include ROM, Flash and battery-packed SDRAM. The CLDC Specification does not define which memory technology a device must have, nor does it define the behavior of such memory in a power-loss scenario.

2. The term volatile is used to indicate that the memory is not expected to retain its contents between the user turning the device "on" or "off". For the purposes of the CLDC Specification, it is assumed that volatile memory can be read and written to directly without any special setup. The most common type of volatile memory is DRAM.

CLDC 8

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