Question

I found the below paragraph in SCJP 6.0 book. What does it mean by the last statement.Which book to read about how these variables are actually stored in memory?. Thanks a lot.

“That’s virtual-machine dependent.”

For boolean types there is not a range; a boolean can be only true or false. If
someone asks you for the bit depth of a boolean, look them straight in the eye and
say, “That’s virtual-machine dependent.” They’ll be impressed.

Answer 1

It means that the only thing required from boolean is to be true or false, no matter what is the underlying implementation.

JLS states:

The boolean type has exactly two values: true and false.

Where for integral types:

The integral types are byte, short, int, and long, whose values are 8-bit, 16-bit, 32-bit and 64-bit signed two’s-complement integers, respectively, and char, whose values are 16-bit unsigned integers representing Unicode characters.

So you have required bit depth for integral types but it is solely up to you if your boolean will be represented in the memory as a single bit, byte or multibyte variable when you implement your own JVM.