This thread looks pretty bizarre. It looks like people are arguing about what is less half-baked than the other. Here's a bit of information for you. In addition, Yellow Box APIs are available through Java. A number of administrative and demo apps are written in Java, to ensure a solid, usable Java environment is shipped.
Carbon presents a procedural interface of C-callable functions.
Some minor changes may be made in these APIs to support the transition. A Carbon compatability library will be made available for MacOS 8 platforms. The API set can be called from compiled programs using the Objective C interface, and from Java programs, courtesy of the curiously similar runtime systems of Objective C and Java and a bit of clever programming. Java, Carbon, and Yellow APIs all share a common set of Core Services, including low level graphics, windowing, events, and memory management services. Development work is continuing on Java, Carbon, and Yellow.