You need a default clause when your cases aren't exhaustive otherwise. The compiler will insert a default clause transparently if you switch over an enum: https

You need a default clause when your cases aren't exhaustive otherwise. The compiler will insert a default clause transparently if you switch over an enum: https://openjdk.java.net/jeps/325 https://openjdk.java.net/jeps/325 The cases of a switch expression must be exhaustive; for any possible value there must be a matching switch label. In practice this normally means simply that a default clause is required; however, in the case of an enum switch expression that covers all known cases (and eventually, switch expressions over sealed types), a default clause can be inserted by the compiler that indicates that the enum definition has changed between compile-time and runtime. (This is what developers do by hand today, but having the compiler insert it is both less intrusive and likely to have a more descriptive error message than the ones written by hand.) This is pretty much the behavior you'd expect if you're familiar with languages that support pattern-matching.