boolean: The boolean data type has only two possible values: true and false. Use this data type for simple flags that track true/false conditions. This data type represents one bit of information, but its "size" isn't something that's precisely defined
Reference:SUN: Primitive Data Types
As i understand it, the BEHAVIOR of things is defined. a boolean must represent 'true' and 'false'. As to the specifics of HOW that happens, that's up to the folks who write the JVM. if they want to do it with a single bit, that's fine. if they want to use 12 bytes, that's fine too. it's up to them.
really, you don't know, and you don't need to know.