Motivation:
- A `hashCode` of the SmtpCommand is recalculated on each call of `hashCode()`. Cached hash code value can be just replaced with call of `name.hashCode()`.
- The commands cache don't work for strings: `SmtpCommand.valueOf("HELO")` returns a new instance.
- Field `contentExpected` is redundant and can be replaced with `equals(DATA)`.
Modifications:
- Use the `name.hashCode()` as hash code result.
- Fix a command cache: use strings as map keys.
- Replace field `contentExpected` to using `this.equals(DATA)`.
- Add unit tests.
Result:
More correct and clean code.
0234878c4b