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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DERBY-6075) Use modern collections in impl/sql/compile
Date Wed, 13 Mar 2013 12:46:13 GMT

     [ https://issues.apache.org/jira/browse/DERBY-6075?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Knut Anders Hatlen updated DERBY-6075:
--------------------------------------

    Attachment: d6075-14a-dead-syntax.diff

There are also some uses of Vector in sqlgrammar.jj, which generates classes that live in
the impl/sql/compile package. Those vectors are private to the thread that's parsing the SQL
statement, as far as I can tell, so it should be safe to replace them with ArrayLists.

Before doing that, I'm attaching a cleanup patch (d6075-14a-dead-syntax.diff) which removes
unneeded import statements from sqlgrammar.jj and removes some dead code that uses vectors.

The removed dead code seems to be there in order to support syntax for declaring columns nullable
explicitly. There is however no such syntax in Derby currently (you can only declare them
nullable implicitly by skipping the NOT NULL constraint), so the following fields and the
code that accesses them are removed:

- explicitNotNull (a boolean)
- explicitNull (a boolean)
- explicitlyNullableColumnsList (a Vector)

The purpose of the fields is to check whether a column is declared explicitly nullable and
not nullable at the same time, and raise an error if so happens. Since there is no way to
declare a column explicitly nullable (evidence: there is no code that sets explicitlyNull
to true, and there is no code that adds elements to explicitlyNullableColumnsList), that's
an impossible situation.

In addition to removing the dead code from sqlgrammar.jj, the patch removes the unused SQLState
and the corresponding error message, including translations.

All tests ran cleanly with the patch.
                
> Use modern collections in impl/sql/compile
> ------------------------------------------
>
>                 Key: DERBY-6075
>                 URL: https://issues.apache.org/jira/browse/DERBY-6075
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.10.0.0
>            Reporter: Knut Anders Hatlen
>            Assignee: Knut Anders Hatlen
>            Priority: Minor
>         Attachments: d6075-10a-aggregate-vectors.diff, d6075-11a-remaining-vectors.diff,
d6075-12a-stack.diff, d6075-13a-unused-properties.diff, d6075-14a-dead-syntax.diff, d6075-1a-CollectNodesVisitor.diff,
d6075-2a-bindExpression.diff, d6075-3a-javadoc.diff, d6075-4a-parameterList.diff, d6075-5a-ordering.diff,
d6075-6a-DMLModStatementNode.diff, d6075-7a-more-signatures.diff, d6075-8a-local-hashtables.diff,
d6075-9a-hashtable-fields.diff
>
>
> The code in the org.apache.derby.impl.sql.compile package predates the Java Collections
Framework and uses old-style collections like java.util.Vector and java.util.Hashtable. Since
the old-style collection classes are used in many method signatures, it's difficult to use
modern collection classes when adding new code.
> I suggest we switch to using interfaces (like java.util.List and java.util.Map) instead
of specific classes in the signatures, so that we have more flexibility in choosing the right
collection class for the job.
> Only changing the signatures would allow us to continue using Vector and Hashtable, since
they implement the interfaces. However, I think it would be good to switch to ArrayList and
HashMap in a second step. The instances in impl/sql/compile are not shared between threads,
so we don't need the synchronization provided by the old-style classes. Switching to unsynchronized
classes may make compilation slightly faster.

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