Tuesday, April 14, 2009

Method Object ^ Param Object

"Essential Java Style" is an excellent text on these 2.

In Both cases, the object is of an inner class. I think the MO need to access the enclosing class's fields (attributes, properties, inst vars).

Both patterns are safe refactor operations, almost blind, robotic operations. I think a computer scientist can prove they won't change behaviour/functionality. Therefore, these are more like implementation patterns than design patterns.

If there are x args to the original VLVU method, then the MO constructor gets exactly those x args, no more no less. All the original inst vars are still accessible from the composed methods in the MO ("inner"), and all original local/stack vars become MO attributes.

When to choose MO over PO? See P34. If after applying composed methods the VLVU method splits to 99 methods, then MO serves to group these many methods inside the inner class, whereas PO leaves them all in the enclosing class.

Note we go to such length just to avoid converting local/stack vars into fields. Such conversions contaminates the original class.

Q: how about a method with too many (55) args?
A: i think you can use an inner class or a regular bean to help build the arg list. Converting all args to attributes is the laziest and dirtiest solution.

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