Implementation of the {@link TextFileCache} interface. This class is abstract; subclasses mustprovide an implementation of the method {@link #getFileName(Object)}, which constructs a filename given an Object identifier that uniquely identifies the data that is to be stored in the corresponding file.
Note: This class is not thread-safe. If an instance of this class is used concurrently by several threads, external synchronization must take place to ensure proper behavior.
@author Torgil Zethson