[jira] [Resolved] (IMPALA-7867) Expose collection interfaces, not implementations

["Marcel Kornacker (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IMPALA-7867?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Marcel Kornacker resolved IMPALA-7867.
--------------------------------------
    Resolution: Won't Fix

The FE code uses specific implementations (ArrayList vs. List) on purpose, in order to guarantee runtime behavior. ArrayList.get() is guaranteed to be O(1), List.get() is not.

> Expose collection interfaces, not implementations
> -------------------------------------------------
>
>                 Key: IMPALA-7867
>                 URL: https://issues.apache.org/jira/browse/IMPALA-7867
>             Project: IMPALA
>          Issue Type: Improvement
>          Components: Frontend
>    Affects Versions: Impala 3.0
>            Reporter: Paul Rogers
>            Assignee: Paul Rogers
>            Priority: Minor
>
> When using Java collections, a common Java best practice is to expose the collection interface, but hide the implementation choice. This pattern allows us to start with a generic implementation (an {{ArrayList}}, say), but evolve to a more specific implementation to achieve certain goals (a {{LinkedList}} or {{ImmutableList}}, say.)
> For whatever reason, the Impala FE code exposes {{ArrayList}}, {{HashMap}} and other implementation choices as variable types and in method signatures.
> This ticket tracks a gradual process of revising the declarations and signatures to use the interfaces {{List}} instead of the implementation {{ArrayList}}.
> Also, the FE code appears to predate Java 7, so that declarations of lists tend to be in one of two forms (with or without Guava):
> {code:java}
> foo1 = new ArrayList<Bar>();
> foo2 = Lists.newArrayList();
> {code}
> Since Java 7, the preferred form is:
> {code:java}
> foo = new ArrayList<>();
> {code}



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