Re: Understanding Exceptions

From:

Lew <noone@lewscanon.com>

Newsgroups:

comp.lang.java.help

Date:

Mon, 08 Nov 2010 07:22:04 -0500

Message-ID:

<ib8q1d$rae$1@news.albasani.net>

On 11/07/2010 05:36 PM, Stanimir Stamenkov wrote:

Sun, 07 Nov 2010 17:08:54 -0500, /Lew/:

Stanimir Stamenkov wrote:

I've always wondered why JAXP, for example, has chosen to throw an Error
from DocumentBuilderFactory.newInstance() [1] and
SAXParserFactory.newInstance() [2]:

Throws:
FactoryConfigurationError - if the implementation is not
available or cannot be instantiated.

Isn't this a similar resource availability situation?

Apparently not in the minds of the JAXP API writers.

[1]
http://download.oracle.com/javase/6/docs/api/javax/xml/parsers/DocumentBuilderFactory.html#newInstance%28%29

[2]
http://download.oracle.com/javase/6/docs/api/javax/xml/parsers/SAXParserFactory.html#newInstance%28%29

Perhaps they see the lack of fundamental class libraries from the Java
runtime as more serious than a failure to plug in a particular
encryption algorithm, in that the former breaks the entire system and
the latter only the situation where you try to open a particular
resource.

The 'NoSuchAlgorithm' situation is closer to a
<http://download.oracle.com/javase/6/docs/api/java/io/FileNotFoundException.html>

than to any kind of 'Error'.

And then 'NoSuchAlgorithm' is implementation detail of the OP's method,

No, it is not. The 'java.security.NoSuchAlgorithmException' is part of the
method signature of 'java.security.MessageDigest.getInstance()', which is part
of the standard API and most definitely not the OP's method.

which he presumably don't want to expose as an API, or at least not as

The Java API writers already exposed it as an API,

checked exception. But he might consider the lack of a particular

.... as a checked exception. That ship has already sailed.

algorithm implementation more than a serious failure which could break
the entire system/application, so is using Error instead of
RuntimeException type in such case generally permissible (not ruled out
completely), if the author thinks it would be better this way?

He might think it is, but the actual author chose to expose it as a checked
exception, the correct approach.

--
Lew