A few thoughts on code quality - mostly for Java, but can be abstracted and used with different technologies.

In my opinion java code of quality should have following properties:

1. Proper naming of classess, methods, variables and constants.
2. Single, properly defined and documented responsibility of each class and method. No unneccessary code (to remove code duplication you can use constants (final keyword, UPPERCASE_NAMES) and split methods with large chunks of code into few smaller methods so you can reuse them. To ensure single responsibility of method or class move some code into another method or class. Single responsibility class or method is more reausable and easier to document, read, test and modify. [or to break if someone wants to try firing quality coder].). Single responsibility of method may involve calling more than one instruction as long as it is considered atomic. For example: changeStateWithSideEffect(...);
3. Documented methods headers (first lines of methods and all information therein, including variable names) according to javadoc documentation.
4. Use of 'assert' keyword, software contracts, preconditions, postconditions and invariants.
5. Fitting 'a complete code part' on a 'single screen', if possible and worthwhile; ... easier thinking, less scrolling, perhaps more.

Later JUnit/Easymock automated tests can be added to build test harness.

Also, code should be properly formatted.

Commits / to code repository, using technologies such as SVN or Git / should be commented.

Methods should be abstract, empty or final.

Ideally, methods should consists of three instructions. init(...); transform(...); return [(...)]; Complex instruction counts as single instruction;

There can be more requirements / for example: coding in idiomatic way / , but in practice it's almost perfect if these are used. Professionals after all have no time to comment code, or they want to be priceless and unfirable by bosses, in a not-so-nice, unfair way.


See also: Design by Contract.