Following a conversation with a friend regarding how ColdFusion handles arrays and structures in ‘the background’, I was interested to find out what Java classes each were mapped to. This was a relatively simple case of using the functions getClass(), getSuperClass() and getName() to parse out the name of the Java classes.

<!--- Arrays (repeat up the hierarchy) --->
<cfdump var="#arrayNew(1).getClass().getName()#">
<cfdump var="#arrayNew(1).getClass().getSuperClass().getName()#">
<!--- Structures (repeat up the hierarchy) --->
<cfdump var="#structNew().getClass().getName()#">
<cfdump var="#structNew().getClass().getSuperClass().getName()#">

What became immediately apparent was that both were handled differently. In the case of a ColdFusion array, the parent class was the java.util.Vector, which seemed obvious. The Vector class implements a growable array of objects. Like an array, it contains components that can be accessed using an integer index. However, the size of a Vector can grow or shrink as needed to accommodate adding and removing items after the Vector has been created.

ColdFusion structures, however, are handled entirely differently, with the parent class being a coldfusion.runtime class. In fact, as we can see below, the code to handle a ColdFusion structure is entirely written for ColdFusion until the root class of java.lang.Object. Clearly ColdFusion does some complex wizardry to handle the complex nature of structues (associative arrays).

The class hierarchy for an Adobe ColdFusion array:

java.lang.Object
	java.util.AbstractCollection
		java.util.AbstractList
			java.util.Vector
				coldfusion.runtime.Array

The class hierarchy for an Adobe ColdFusion structure:

java.lang.Object
	coldfusion.util.CaseInsensitiveMap
		coldfusion.util.FastHashtable
			coldfusion.runtime.Struct

Being an inquisitive person, I applied the same code to Railo and BlueDragon, with equally interesting results.

The Java class hierarchy behind a Railo array:

java.lang.Object
	railo.runtime.type.ArrayImpl

The Java class hierarchy behind a Railo structure:

java.lang.Object
	railo.runtime.type.StructImpl

The Java class hierarchy behind a BlueDragon array:

java.lang.Object
	com.naryx.tagfusion.cfm.engine.cfData
		com.naryx.tagfusion.cfm.engine.cfJavaObjectData
			com.naryx.tagfusion.cfm.engine.cfArrayData
				com.naryx.tagfusion.cfm.engine.cfArrayListData

The Java class hierarchy behind a BlueDragon structure:

java.lang.Object
	com.naryx.tagfusion.cfm.engine.cfData
		com.naryx.tagfusion.cfm.engine.cfJavaObjectData
			com.naryx.tagfusion.cfm.engine.cfStructData

Adendum: Ben Nadel has a good little post on ColdFusion Data Types from Different Sources and How ColdFusion Sees Them.