The previous section used the Fqn class in its examples; now let's learn a bit more about that class.

A Fully Qualified Name (Fqn) encapsulates a list of names which represent a path to a particular location in the cache's tree structure. The elements in the list are typically String s but can be any Object or a mix of different types.

This path can be absolute (i.e., relative to the root node), or relative to any node in the cache. Reading the documentation on each API call that makes use of Fqn will tell you whether the API expects a relative or absolute Fqn .

The Fqn class provides are variety of constructors; see the javadoc for all the possibilities. The following illustrates the most commonly used approaches to creating an Fqn:

   // Create an Fqn pointing to node 'Joe' under parent node 'Smith'

   // under the 'people' section of the tree

        

   // Parse it from a String

   Fqn<String> abc = Fqn.fromString("/people/Smith/Joe/");

        

   // Build it directly. Marginally more efficient to construct than parsing

   String[] strings = new String[] { "people", "Smith", "Joe" };

   Fqn<String> abc = new Fqn<String>(strings);

        

   // Here we want to use types other than String

   Object[] objs = new Object[]{ "accounts", "NY", new Integer(12345) };

   Fqn<Object> acctFqn = new Fqn<Object>(objs);

     

Note that

Fqn<String> f = new Fqn<String>("/a/b/c");

is not the same as

Fqn<String> f = Fqn.fromString("/a/b/c");

The former will result in an Fqn with a single element, called "/a/b/c" which hangs directly under the cache root. The latter will result in a 3 element Fqn, where "c" idicates a child of "b", which is a child of "a", and "a" hangs off the cache root. Another way to look at it is that the "/" separarator is only parsed when it forms part of a String passed in to Fqn.fromString() and not otherwise.

The JBoss Cache API in the 1.x releases included many overloaded convenience methods that took a string in the /a/b/c format in place of an Fqn . In the interests of API simplicity, no such convenience methods are available in the JBC 2.x API.