It doesn't have a defined size.  A Java implementation is free to store a
boolean in any fashion that it chooses.

It is up to the individual JVM implementation. It is possible that
different amounts of memory will be allocated in different situations.
However, the case that is both most interesting and most measurable is a
large boolean[] array.

I've previously measured it as one byte per element, rounded up to a
multiple of 8 and plus 8 bytes per array overhead. However, your mileage
may vary, and if you really need to know you should measure it on the
system you care about.

Patricia