RFR 8168979: @implNote for invalid FilePermission

[Wang Weijun]

> On Dec 14, 2016, at 10:11 AM, Xuelei Fan <xuelei.fan at oracle.com> wrote:
> 
> On 12/13/2016 5:45 PM, Wang Weijun wrote:
>> A major behavior change is that <<ALL FILES>> now implies an invalid permission, I hope this is good to minimize incompatibility.
> Looks like two sides of the same coin.  If there is an invalid <<ALL FILES>> (not existing in practice, I think),

Not existing in theory either. As the change says, invalid happens when the conversion of string to NIO Path fails. For <<ALL FILES>>, there will be no such conversion.

> it now implies all;  if no change on this point, <<ALL FILES>> does not imply invalid one.  The existing behavior looks more safe to me.  What's you concern to make this behavior change?

Just safer. Sometimes an app can recover from a FileNotExistException but not a SecurityException.

Thanks
Max

> 
> Otherwise, looks fine to me.
> 
> Xuelei