> For the complete documentation index, see [llms.txt](https://petozoltan.gitbook.io/simplecode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://petozoltan.gitbook.io/simplecode/clean-code/clean-code-outline/error-handling.md).

# Error Handling

### Two types of exceptions

* Expected or business exceptions \~ *checked?*
* Unexpected program or environment errors \~ *unchecked?*

### Good Practices

* Prefer exceptions to return codes - *decreases pollution of clients*
* Prefer exception types to exception payload - *error codes*
* Provide context for exception:
  * chain exceptions when wrapping
  * add erroneous object(s)
* Do not return null - *throw exception (e.g. IllegalArgumentException)*
* Prefer runtime exceptions to checked exceptions - *decreases pollution and dependency*
* Wrap exceptions in module or service specific exceptions - *decrease dependency*
* Only unexpected exceptions should be logged on error level with stack-trace.

### Bad Practices

* Swallow exceptions
* Implement business logic in catch block
* Do not catch exceptions unless you handle them
* `handleError()` type of methods -
  * *not readable what they do*
  * *they cheat the compiler too*