Question

Reverse array elements in coldfusion

Asked by: WyleOP

ColdFusion version: CF9

I'm trying to reverse the order of the elements in an array (columns in a result set).  I've tried:

<cfset columns = mtbf.getColumnNames()>
<cfscript>
      createObject("java", "java.util.Collections").reverse(columns);
</cfscript>

But I get...

The reverse method was not found.  
Either there are no methods with the specified method name and argument types or the reverse method is overloaded with argument types that ColdFusion cannot decipher reliably. ColdFusion found 0 methods that match the provided arguments. If this is a Java object and you verified that the method exists, use the javacast function to reduce ambiguity.  


If I try and cast the array using JavaCast using,

<cfset columns = mtbf.getColumnNames()>
<cfset stringArr = Javacast("string[]",columns)/>


I get...

JavaCast type string[] must be one of the following types: byte, char, short, int, long, float, double, boolean, string, bigdecimal, their corresponding array representation (eg : int[]), or null.

Any thoughts?

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Asked On
2009-11-05 at 07:31:41ID24874759
Tags

Coldfusion

Topic

ColdFusion Application Server

Participating Experts
3
Points
500
Comments
5

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Answers

 

by: plusone3055Posted on 2009-11-05 at 10:06:02ID: 25752146

 

by: WyleOPPosted on 2009-11-05 at 10:15:16ID: 25752238

 

by: SidFishesPosted on 2009-11-05 at 12:09:40ID: 25753402

I wonder if columns is actually an array

if you try this example from http://www.barneyb.com/barneyblog/?s=batik+transcod

<cfscript>
 a = [1, 2, 3, 4, 5, 1, 2, 3, 4, 5];
// reverse it
createObject("java", "java.util.Collections").reverse(a);
writeOutput(a.toString()); // [5, 4, 3, 2, 1, 5, 4, 3, 2, 1]

// sort it
createObject("java", "java.util.Collections").sort(a);
writeOutput(a.toString()); // [1, 1, 2, 2, 3, 3, 4, 4, 5, 5]

// pull unique elements
a = createObject("java", "java.util.ArrayList").init(
  createObject("java", "java.util.HashSet").init(a)
);
writeOutput(a.toString()); // [3, 2, 1, 5, 4]

// unique elements in sorted order
createObject("java", "java.util.Collections").sort(a);
writeOutput(a.toString()); // [1, 2, 3, 4, 5]
</cfscript>

you can see that reverse is valid and does work as expected...



 

by: _agx_Posted on 2009-11-05 at 12:28:25ID: 25753615

> <cfset columns = mtbf.getColumnNames()>
>  createObject("java", "java.util.Collections").reverse(columns);
> Any thoughts?

Subtle but important difference.  getColumnNames() returns a string array. reverse() expects a java.util.List. Not the same thing. That's why you're getting an error.

To make it work you'd have to convert the string[] array to a List, reverse it, then convert it back to a string[] array. Given all that ... it seems simpler to just do the reverse yourself in CF.  

BTW-Just remember #columns# is a java array.. not a CF array.

<cfset columns = mtbf.getColumnNames()>
<cfdump var="#columns#" label="Before">
<cfscript>
   list = createObject("java", "java.util.Arrays").asList(columns);
   createObject("java", "java.util.Collections").reverse(list);
   newColumns = list.toArray();
</cfscript>
<cfdump var="#newColumns#" label="After">

                                              
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by: WyleOPPosted on 2009-11-06 at 04:22:57ID: 31650534

Great job.  You always rise above the mediocrity of others.

20120131-EE-VQP-002

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