The JSR14 protptype (2.0) has some problems in the implementation of
boxing and unboxing:

(1) boxing/unboxing as an assignment conversion was not properly handled.

(2) boxing/unboxing as a cast conversion was not properly handled.

(3) unboxing should not go to the "desired" target type, but rather to
the appropriate unboxed type based on the type of the box.

(4) primitive conversions before boxing should just work:
Double d = 2;