Hi Joe,
On 04/22/2016 07:47 PM, joe darcy wrote:
Hi Roger,
Per other discussion in the thread, no new method will be introduced.
The area owners will need to cleanup this usage of this method since
it may involve restructuring of catch blocks, etc., since the
recommended approach has different exception behavior.
The functionality of Class.newInstance() might have a logical
replacement in existing API (getConstructor().newInstance()) but this
replacement is not equivalent performance-wise.
As mentioned, Class.newInstance() has a special cache for constructor
and caller that speeds up repeated invocations from the same caller by
skipping access checks. Suppose there exist a public API like the following:
public <T extends SomeType> T instantiateAndSetup(Class<T> clazz) { ... }
...that uses clazz.newInstance() inside the implementation to construct
new instances of passed-in classes. Suppose such API is widely used and
is performance sensitive. What is the maintainer of that API supposed to
do when Class.newInstance() is deprecated and later removed with no
replacement? He has the following choices:
- deprecate his API and provide a replacement taking a Constructor
object instead of a Class object and leave the responsibility of
Constructor(s) caching to the user of the API.
- maintain an internal cache of Class -> Constructor in his
implementation of the API. Such cache is not trivial as it must weakly
reference Class and Constructor objects or ClassLoader leaks are
possible and it has its own overhead.
Wouldn't it be possible to just change the specification of the method
to wrap checked exceptions with an unchecked exception (such as
UdeclaredThrowableException)? I think this would have a minimal impact
on existing code as constructors usually don't throw checked exceptions
- in particular the no-argument constructors.
Is there any evidence that such no-argument constructors exist at all,
let alone that they are invoked via Class.newInstance() ?
Regards, Peter
Thanks,
-Joe
On 4/22/2016 8:33 AM, Roger Riggs wrote:
Hi Joe,
Wouldn't it be less make work to introduce the new method, replace
the current one where appropriate
and then deprecate the existing method? As it is, you/someone is
going to make a second pass
over all the same files.
Roger
On 4/21/2016 12:25 PM, joe darcy wrote:
Hello,
After a generally positive reception, please review the webrev to
implement the deprecation of Class.newInstance and the suppression
of the resulting warnings:
http://cr.openjdk.java.net/~darcy/6850612.0/
There are also some changes in the langtools repo; I'll send a
separate review request for those changes to compiler-dev.
I'll also forward this review request to other areas with affected
code.
Thanks,
-Joe
On 4/17/2016 10:31 AM, joe darcy wrote:
Hello,
With talk of deprecation in the air [1], I thought it would be a
fine time to examine one of the bugs on my list
JDK-6850612: Deprecate Class.newInstance since it violates the
checked exception language contract
As the title of the bug implies, The Class.newInstance method
knowingly violates the checking exception contract. This has long
been documented in its specification:
Note that this method propagates any exception thrown by the
nullary constructor, including a checked exception. Use of this
method effectively bypasses the compile-time exception checking
that would otherwise be performed by the compiler. The
Constructor.newInstance method avoids this problem by wrapping any
exception thrown by the constructor in a (checked)
InvocationTargetException.
Roughly, the fix would be to turn the text of this note into the
@deprecated text and to add a @Deprecated(since="9") annotation to
the method. There are a few dozen uses of the method in the JDK
that would have to be @SuppressWarning-ed or otherwise updated.
Thoughts on the appropriateness of deprecating this method at this
time?
Comments on the bug have suggested that besides deprecating the
method, a new method on Class could be introduced,
newInstanceWithProperExceptionBehavior, that had the same signature
but wrapped exceptions thrown by the constructor call in the same
way Constructor.newInstance does.
Thanks,
-Joe
[1]
http://mail.openjdk.java.net/pipermail/core-libs-dev/2016-April/040192.html
