The requirement for a final default clause is defensive programming. This clause should either take appropriate action or contain a suitable comment as to why no action is taken.

The following code snippet illustrates this rule:

switch (state) {                       // Non-Compliant - must have a default case
  case 0:
  case 1:
    System.out.println("0 or 1!");
    break;
}

switch (state) {
  default:                             // Non-Compliant - must be last for better readability
    throw new IllegalStateException();
  case 0:
  case 1:
    System.out.println("0 or 1!");
    break;
}

switch (state) {
  case 0:
  case 1:
    System.out.println("0 or 1!");
    break;
  default:                             // Compliant
    throw new IllegalStateException();