Why is “public” not allowed for properties in JPA entities?

Question

The JPA 2.0 specification says on page 22:

The instance variables of a class must be private, protected, or package visibility independent of whet

Answer 1

With public fields, there would be no way for proxying to work reliably -- if someone accesses a field directly, then there is no simple way for the persistence framework to intercept that call and (say) initialize the containing object, if it's a proxy.

If field access is not possible, synthetic getter methods can be generated on the proxy object to intercept the method calls and do any required 'behind-the-scenes' work.