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J2ME Historical events:
1998:

• Sun refocused on mobile and entertainment devices (Java's original intention)
• Released pJava to be used for resource constrained devices.
• pJava was based on core set of JDK1.1.8 and some new API’s specific to mobile devices.
• Though pJava fit bigger devices such as setboxes better, it did a poor job on other smaller devices.

• Sun creates a VM for Palm Pilots.
• The project was called "Spotless", and the VM created became KVM.
• KVM together with Spotlet demo was released for early access at JavaOne.
• It was standardized via JCP, and came out as a set of configurations and profiles, with a new name J2ME.
• J2ME release overcame the inefficiencies of pJava.

• Sun extends pJava for handsets (PDAs and SmartPhones) with a JavaPhone API which found its way into several Symbian OS 6 implementations.
• These extensions became new classes in J2ME via PP and the PBP.

• Nextel Communications, Inc. introduces first java enabled wireless phone in North America.
• The i85s, manufactured by Motorola, is pre-loaded with Java apps, including specialized business calculators and an expense pad.Allows download of J2ME applications.

• Memory (Persistent & Volatile).
• Processing speed
• Output device
• Input device
• Network connectivity
• Power supply

• It defines the minimum platform required for a group of devices.
• It defines a lowest common denominator J2ME Runtime Environment.
• It includes VM and a set of common API derived primarily from J2SE.
• Each configuration is geared for a family of devices with similar capabilities.
• Two configurations have been defined:
• Connected Device Configuration (CDC).
• Connected, Limited Device Configuration (CLDC)

• Designed for devices with a min of 512KB of memory (ROM) and 256KB of RAM.
• Specifies a full Java Virtual Machine called CVM.
• Total memory budget range may extend
• up to 16MB.
• CDC compliant devices may have 16 or 32 bit CPUs.
• E.g. TV Set-top boxes, Car navigation systems, RTS, Washing Machine etc.
  

• 128kb memory for Java
• 32kb for runtime allocation
• Restricted UI
• Low bandwidth network connectivity, intermittent access
• KVM is reference implementation
• E.g. Mobile Devices, PDA

• Kilo Virtual Machine (KVM) a minimal and almost complete JVM, small enough to fit in tens of kilobytes.
• Lots of features eliminated
• floating point, finalize(), JNI, etc.
• Change in classfile verification
• Preverifier, verifier
• Classfile format: JAR

• Compack Virtual Machine
• JVM with J2SE 1.3 VM specification compliancy.
• Supports almost all advanced features of J2SE VM, including low-level debugging and native programming interfaces.
• It is more portable, more efficient, and smaller than J2SE VM.
• CVM was written in C and uses a portability layer to abstract underlying OS dependencies.
• CVM improves garbage collectors, native-thread support, synchronization, and stack usage.

• 128 kb non-volatile memory
• 32 kb volatile memory
• 8 kb of non-volatile memory for persistency
• A screen of at least 96 x 54 pixels
• Some capacity for input
• Two-way network connection, possibly intermittent

• Instantiation
• pauseApp()
• startApp()
• destroyApp()
• Deallocation