Hello,
On 4/22/2020 6:12 AM, Alan Bateman wrote:
On 22/04/2020 13:50, Andrew Haley wrote:
:
1. Should close() always be idempotent, where practical? I would have
thought so, but perhaps there are downsides.
2. Should classes which implement close() with the standard meaning be
AutoCloseable?
I'm sure Joe Darcy can say more on this but I remember there was a lot
of effort put into this topic when AutoCloseable was added in Java 7
(and Project Coin). Closeable close is idempotent but AutoCloseable
close could not require it. AutoCloseable's API docs recommend it of
course. There was effort in Java 7 and beyond to retrofit existing
classes that defined a close method to be Closeable or AutoCloseable.
There are only a handful of exported APIs remaining that have a close
method that don't extend or implement AutoCloseable. I don't know the
history of the XML stream interface to know why they close to define
them not to close the underlying stream but I doubt these could be
changed now.
Yes, the JSR 334 EG had some discussions about both "SilentCloseable"
(no exceptions) and "IdempotentCloseable" as possible library additions
back in the JDK 7 time frame. These were not judged to have sufficient
marginal utility over Closeable and AutoCloseable to include in the
platform.
It was impractical to require idempotent close methods in call cases,
but they are recommended. Generally, a type with a void close method
should implement AutoClosable. Most of the candidate types in the JDK
were updated for JDK 7; a few stragglers were updated since then, but
there are a few remaining cases that could be updated as discussed
earlier in this thread.
HTH,
-Joe
