In all the above sections, the cascading.operation.BaseOperation class was subclassed. This class is an implementation of the cascading.operation.Operation interface and provides a few default method implementations. It is not strictly required to extendBaseOperation, but it is very convenient to do so.

When developing custom operations, the developer may need to initialize and destroy a resource. For example, when doing pattern matching, a java.util.regex.Matcher may need to be initialized and used in a thread-safe way. Or a remote connection may need to be opened and eventually closed. But for performance reasons, the operation should not create/destroy the connection for each Tuple or every Tuple group that passes through.

The interface Operation declares two methods, prepare() and cleanup(). In the case of Hadoop and MapReduce, the prepare() and cleanup() methods are called once per Map or Reduce task. prepare() is called before any argument Tuple is passed in, and cleanup() is called after all Tuple arguments have been operated on. Within each of these methods, the developer can initialize a "context" object that can hold an open socket connection, or Matcher instance. The "context" is user defined and is the same mechanism used by the Aggregator operation, except the Aggregator is also given the opportunity to initialize and destroy its context via the start() and complete() methods.

If a "context" object is used, its type should be declared in the sub-class class declaration using the Java Generics notation.