A Transformer with the default operation to narrow the type of the visited subject; all methods for abstract node types have a default implementation while those for concrete node types remain formal.

There are two ways to perform this narrowing:

• immediately, by invoking the transform (Node.transform) method on the subject, or
• cascadingly, where each method switches on the enumerated subtypes of the node type and narrows only by one layer by invoking the corresponding transformX method on the transformer.

It should be possible to use them interchangeably (swap out the satisfying type of your implementing class without any effect), and since the immediate version is faster (it’s only a virtual method lookup instead of a series of calls and type checks), you should probably use that.