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The Good Citzen Object
Posted about over 2 years ago
The picoContainer website (a lightweight IoC container) has some really good information about class design. One page in particular nails some solid points and I think it is good for all developers to review it.
As a good citizen, I…
- Keep a consistent state at all times - init() or populate() is a code smell.
- Have no static fields or methods
- Never expect or return null.
- FailFast - even when constructing.
- Am Easy to test- all dependent object I use can be passed to me, often in my constructor (typically as Mock Objects).
- Accept dependent object that can easily be substituted with Mock Objects (I don't use Concrete Class Dependency).
- Chain multiple constructors to a common place (using this(...)).
- Always define hashCode() alongside equals()
- Prefer immutable value objects that I can easily throw away.
- Have a special value for 'nothing' - e.g. Collections.EMPTY_SET.
- Raise checked exceptions when the caller asked for something unreasonable - e.g. open a non-existant file.
- Raise unchecked exceptions when I can't do something reasonable that the caller asked of me - e.g. disk error when reading from an opened file.
- Only catch exceptions that can be handled fully.
- Only log information that someone needs to see.