DiagnosticCode

```
public interface DiagnosticCode
```
A DiagnosticCode is a unique identifier that the compiler can associate with a diagnostic. This is useful for tools to be able to quickly identify what diagnostic is being reported without having to rely on parsing the actual diagnostic message, which might not be stable.

All Methods Instance Methods Abstract Methods
Modifier and Type	Method and Description
`java.lang.String`	`code()` The unique code.
`java.util.Optional<java.lang.String>`	`explanation()` Possible explanation to explain the meaning of the code

Interface DiagnosticCode