Hi,

While working on a small refactoring in the Kudu Java client, I found
that sometimes we use asserts
and sometimes Preconditions [2] from the guava library to assert on the
consistency of the code.

As Todd suggested, I'm starting this thread to clarify on what is the
best way to do perform
the consistency checks in our Kudu Java client code.  Ideally, the
desired outcome from the
anticipated discussion would be some sort of guidance on assertion of
the consistency constrains
and invariants in our Java client code.  Once we have the guidance, we
could put it as an
additional section of our 'Contributing' page.

The issue with the Java asserts is that they are not applicable unless
the JVM is run with '-ea'
flag, so it's not possible to explicitly stop processing further
instructions in the context
when an inconsistency is detected.

To me, we have more clarity with the consistency checks and invariant
assertion in our C++ code.
We have CHECK- and DCHECK- derived macros to perform various types of
consistency checks.  In short,
the CHECK-related are always there, and the DCHECK-related ones are
present only in debug builds.
We don't turn on/off any of those dynamically in runtime.  Also, those
C++ asserts are kind of 'hard'
ones -- the whole program is terminated and you don't need to think how
to deal with the mess which
isn't possible to recover from.  The latter one is a luxury which is not
available in Java
(correct me if I'm wrong).

Putting the explicit termination of the whole program (with an optional
coredump) aside,
the Java's assert looks like DCHECK() but with the ability to turn it
on/off using the run-time switch.
Using guava's Preconditions gives us an option to address that and have
a way
to assert the consistency in our code even if code is run without the
'-ea' JVM flag.

So, to me it looks natural to use the Preconditions-derived checks for
asserting on invariants
even while running in production environment, while using asserts only
in debug/test mode,
asserting on programmatic errors and other non-crucial invariants which
might be handled
by the code even if those checks are removed.

However, this simple approach contradicts to some points of [1] (which,
by my understanding,
is contradictory and very confusing as is).  Also, I'm not a Java
programmer,
so I might be missing some crucial points here.

What do you think?  Your feedback is highly appreciated.
Thanks,

Alexey
References:
   [1]
http://docs.oracle.com/javase/8/docs/technotes/guides/language/assert.html
   [2] https://github.com/google/guava/wiki/PreconditionsExplained
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