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From "Levon Karayan (JIRA)" <>
Subject [jira] Commented: (LANG-534) ArrayUtils should have method to convert null arrays to empty ones to help with Defensive coding
Date Thu, 24 Sep 2009 20:50:16 GMT


Levon Karayan commented on LANG-534:

I think the advantage of preventing memory fragmentation is a good one and would like to keep
that feature.   That's harder to do with generics/primitives.

However I also like the idea of having a generic version for everything else, I chose not
to include it in this patch because my implementation would emit a warning during compile,
or as Matt pointed out we would have to have the user pass it in.   If the user passes in
the empty array and there is no benefit  (actually a disadvantage because your creating garbage
for most cases) for memory from using the *public static final* data members already in the
*ArrayUtils* class it defeats the purpose.

{code:title=Generic nullToEmpty}
public static <T> T[] nullToEmpty(T[] array) {
    return (null == array) ? (T[])(new Object[0]) : array;

The problem with this implementation is that you would suddenly have this compile time warning:
{code:title=Generic Array Creation Trick Warning}
[WARNING] /home/foo/proj/opensource/commonslang/src/java/org/apache/commons/lang/[438,38]
[unchecked] unchecked cast
found   : java.lang.Object[]
required: T[]

I can create a new patch that includes the above if the commiters think that is acceptable.

> ArrayUtils should have method to convert null arrays to empty ones to help with Defensive
> ------------------------------------------------------------------------------------------------
>                 Key: LANG-534
>                 URL:
>             Project: Commons Lang
>          Issue Type: Improvement
>            Reporter: Levon Karayan
>            Priority: Trivial
>         Attachments: 20090920LevonArrayUtils-nullToEmpty.patch
> There are APIs that I've come across that return <code>null</code> Arrays
in the event where there are no results.  Often these APIs correctly throw exceptions when
there is an "exceptional event", but no results isn't exceptional, and it often shouldn't
be.   This causes the programmer to make extra tests for null throughout the code to deal
with the null case, and sometimes these null cases are added after a customer searched for
gobleygook and got a NullPointerException.  It's just far cleaner/safer to convert these null
arrays to empty arrays.
> Another benefit to this method is that if the array being passed in is actually already
an empty array, it will swap the pointer for the <code>static final</code> in
the ArrayUtils class to help decrease memory fragmentation.
> e.g.
> try
> {
>   results = customer.getResults(query);
> } catch ( IOException ioex ) {
>   //  ...
> }
> if ( null == results )
> {
>    results = new int[0]{};
> }
> // do stuff
> try
> {
>   results = ArrayUtils.nullToEmpty(customer.getResults(query));
> } catch ( IOException ioex ) {
>   //  ...
> }
> // do stuff

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