A loop-switch sequence (also known as the for-case paradigmThe FOR-CASE paradigm and Switched on Loops at The Daily WTF or Anti-Duff's Device) is a programming antipattern where a clear set of steps is implemented as a switch-within-a-loop. The loop-switch sequence is a specific derivative of spaghetti code.
It is not necessarily an antipattern to use a switch statement within a loop—it is only considered incorrect when used to model a known sequence of steps. The most common example of the correct use of a switch within a loop is an inversion of control such as an event handler. In event handler loops, the sequence of events is not known at compile-time, so the repeated switch is both necessary and correct (see event-driven programming, event loop and event-driven finite state machine).
This is not a performance antipattern, though it may lead to an inconsequential performance penalty due to the lack of an unrolled loop. Rather, it is a clarity antipattern, as in any non-trivial example it is much more difficult to decipher the intent and actual function of the code than the more straightforward refactored solution.
Example
An event-driven solution would implement a listener interface: String key = null; String value = null; List<String> params = null; int column = 0;
public void addToken(token) {
// parse a key, a value, then three parameters switch (column) { case 0: params = new LinkedList<String>(); key = token; break; case 1: value = token; break; default: params.add(token); break;
if (++column >= 5) { column = 0; completeRow(key, value, params);
But without the listener, it becomes an example of the antipattern: // parse a key, a value, then three parameters String key = null; String value = null; List<String> params = new LinkedList<String>();
for (int i = 0; i < 5; i++) { switch (i) { case 0: key = stream.parse(); break; case 1: value = stream.parse(); break; default: params.add(stream.parse()); break;
And here is the refactored solution: // parse a key and value String key = stream.parse(); String value = stream.parse();
// parse 3 parameters List<String> params = new LinkedList<String>(); for (int i = 0; i < 3; i++) { params.add(stream.parse()); }
References