Rule java:S128 flags switch cases without a terminating break (or other exit condition such as return or throw).
Sometimes the “fallthrough” is deliberate. Some versions of this rule in other languages (cpp for one), make exceptions for when a standard annotation is used for marking a fallthrough as intentional. It would be nice to add this capability to java:S128. Unfortunately, Java doesn’t have a standard way to do this. (There apparently is some kind of annotation but it only works at method granularity.) There are various schemes in some style guides but they aren’t universally used. So it would need a parameter with a regex. For max flexibility it should look at either the line with the case label or the line above.