#377 UseArraysAsListInsteadOfTightLoops

[Fabio Insaccanebbia]

When we have to pass between "Object arrays" and List
we should use the utility classe Arrays.

This should give us two advanatges:

• less code
• (slightly better) performance
  [in the JDK implementation the array becomes the "inner
  data structure" of the List implementation that is
  returned.. no copy]

-- before
List arrList = new ArrayList();

for (int i=0;i< MAX; i++) {
arrList.add(arr[i]);
}

-- after
List arrList = Arrays.asList(arr);

I might try writing this rule with an xpath expression..

[Fabio Insaccanebbia]

Logged In: YES
user_id=762447

OK, not easy :-(

//Statement[(ForStatement) and (count(.//IfStatement)
=0)]//StatementExpression
[PrimaryExpression/PrimaryPrefix/Name
[@Image = concat
(ancestor::MethodDeclaration//LocalVariableDeclaration
[./Type//ClassOrInterfaceType[@Image = 'List' or @Image
= 'ArrayList']]/VariableDeclarator/VariableDeclaratorId
[count(..//AllocationExpression/ClassOrInterfaceType
[@Image="ArrayList"])=1]/@Image,".add")]
and
PrimaryExpression/PrimarySuffix/Arguments/ArgumentList/Expre
ssion/
PrimaryExpression/PrimaryPrefix/Name
[@Image =
ancestor::MethodDeclaration//LocalVariableDeclaration
[@Array="true"]/VariableDeclarator/VariableDeclaratorId/@Ima
ge]
/../..[count(.//PrimarySuffix)
=1]/PrimarySuffix/Expression/PrimaryExpression/PrimaryPrefix
/Name
]

The XML rule

<rule name="UseArraysAsList" message="Use asList instead of tight loops" class="">
<description>
The class java.util.Arrays has a "asList" method that
should be use when you want to create a new List from
an array of objects. It is faster than executing a loop to
cpy all the elements of the array one by one
</description>
<properties>
<property name="xpath">
<value></value></property></properties></rule>

</value>
</property>

<priority>3</priority>
<example></example>

[Tom Copeland]

Logged In: YES
user_id=5159

Moving to 'patches', thanks Fabio!

tom

[Tom Copeland]

Logged In: YES
user_id=5159

Committed to CVS, and you can download a new pmd-3.4.jar
file here:

http://infoether.com/~tom/pmd-3.4.jar

that contains this rule in the optimizations ruleset.

Thanks Fabio!

Yours,

Tom
Using PMD? Get the book, "PMD Applied"! http://pmdapplied.com/