Java 2 Platform, Micro Edition (J2ME), is a platform developed by Sun Microsystems (now owned by Oracle) for building applications and services for resource-constrained embedded systems, such as mobile phones, PDAs (Personal Digital Assistants), and other small computing devices. J2ME was particularly popular in the early days of mobile app development before the advent of modern smartphone platforms like Android and iOS. Here are some key aspects of J2ME:

1. Configurations and Profiles: J2ME is based on the concept of Configurations and Profiles. Configurations define the minimum requirements for a particular category of devices (e.g., CLDC – Connected Limited Device Configuration), and Profiles provide additional APIs and libraries for specific types of devices (e.g., MIDP – Mobile Information Device Profile).

2. Development Environment: J2ME applications were typically developed using Java programming language and a specialized development environment such as the Sun Java Wireless Toolkit or the EclipseME plugin. These tools provided emulators for testing applications on various virtual devices.

3. Limited Resources: J2ME was designed for devices with limited processing power, memory, and screen size. Therefore, applications had to be optimized for resource efficiency.

4. Mobile Games and Apps: J2ME was widely used for developing mobile games and small utility applications for feature phones and early smartphones. Many classic mobile games were built using J2ME.

5. Platform Fragmentation: One challenge with J2ME was platform fragmentation. Different devices and manufacturers often had their own implementations of J2ME, which led to compatibility issues for developers.

6. Java ME (Micro Edition): J2ME evolved into Java ME (Micro Edition), which included updates and improvements. However, the popularity of Java ME declined as modern smartphone platforms like Android and iOS gained prominence.

7. End of Life: Oracle officially announced the end of commercial support for Java ME in  marking the end of an era for this platform. Developers have since shifted their focus to more modern mobile app development technologies.

While J2ME is no longer a primary platform for mobile app development, it played a significant role in the history of mobile computing and provided a foundation for understanding mobile development concepts. Today, mobile app development primarily revolves around platforms like Android and iOS, but Java’s influence on mobile development remains significant.