Why finalize is declared protected instead of public?

making finalize protected looks good in terms of following rule of encapsulation which starts with least restrictive access modifier like private but making finalize private prevents it from being overridden in subclass as you can not override private methods, so making it protected is next obvious choice.

2) One of the most important points of finalize method is that it's not automatically chained like constructors. If you are overriding finalize method then it's your responsibility to call finalize() method of the superclass, if you forgot to call then finalize of super class will never be called.

3) finalize method is called by garbage collection thread before collecting object and if not intended to be called like a normal method.

4) finalize gets called only once by GC thread if object revives itself from finalize method than finalize will not be called again.

5) Any Exception is thrown by finalize method is ignored by GC thread and it will not be propagated further, in fact, I doubt if you find any trace of it.