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Java Canonicaliser


This essay does not describe an existing computer program, just one that should exist. This essay is about a suggested student project in Java programming. This essay gives a rough overview of how it might work. I have no source, object, specifications, file layouts or anything else useful to implementing this project. Everything I have prepared to help you is right here.

This project outline is not like the artificial, tidy little problems you are spoon-fed in school, when all the facts you need are included, nothing extraneous is mentioned, the answer is fully specified, along with hints to nudge you toward a single expected canonical solution. This project is much more like the real world of messy problems where it is up to you to fully the define the end point, or a series of ever more difficult versions of this project and research the information yourself to solve them.

Everything I have to say to help you with this project is written below. I am not prepared to help you implement it; or give you any additional materials. I have too many other projects of my own.

Though I am a programmer by profession, I don’t do people’s homework for them. That just robs them of an education.

You have my full permission to implement this project in any way you please and to keep all the profits from your endeavour.

Please do not email me about this project without reading the disclaimer above.

Here are three exercises in writing a parser, probably using JavaCC. Each project is designed to tidy a Java source program to make it easier to read, easier to navigate and easier to debug. It also makes it easier to compare two similar programs for differences or two versions of the same program for differences. The intent of canoncalisation is to remove differences that don’t matter by tidying equivalent programs into a unique standard form.

The first project, to put Java keywords in canonical order, (e.g. public static final), has already been documented elsewhere.

The next most difficult project is to reorder enum constants in alphabetical order. You can’t integrate such a beautification into a standard beautifier since it changes the semantics of a program. The ordinal() values will change. The ordinals in an SQL (Standard Query Language) database for example would be scrambled to associated with different enum constants. There are many cases where that is not a problem and you do want the enums maintained in alphabetical order. This can be a chore. browse source in repository

The most difficult is to put case statements in canonical order. This order is defined as: by ordinal for enums, by numerical value for numeric literals and in alphabetical order for named constants. The case statements above each bit of switch code are sorted in order. The blocks of switch code are sorted in order by the value of the first case statement.

If there is a missing break, a fall-thru, here are two ways to handle it.

  1. Throw up your hands and refuse to sort the case statements.
  2. Lock together chunks of code without a break and move them as a unit, sorting the two sets of case statements for the unit independently. The unit as a whole is sorted into position by the value of its first case.
Test your beautifier with all three types of comments embedded and also some @annotations.
canonical keyword order project

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