I have experience with grammars, but not with the Java one. There isn't an inherent restriction on context-free grammars why this couldn't happen. In pseudocod

I have experience with grammars, but not with the Java one. There isn't an inherent restriction on context-free grammars why this couldn't happen. In pseudocode this could work fine: classDef = accessModifier? classModifier* `class` identifier `{` (fieldDef|methodDef|classDef)* `}` fieldDef = accessModifier? fieldModifier* type identifier `=` expression classModifier = `data` fieldModifier = `synchronized` | `final` | `volatile` As you can see there isn't an inherent reason why the identifier rule should exclude the `data` keyword for this to work