code: @Deprecated
      public Collection<String> getRedundants(Collection<String> output) {
          synchronized (this) { // synchronized since a getter must be thread-safe
              if (output == null) {
                  output = new LinkedHashSet<String>();
              }
              for (DateTimeMatcher cur : skeleton2pattern.keySet()) {
                  PatternWithSkeletonFlag patternWithSkelFlag = skeleton2pattern.get(cur);
                  String pattern = patternWithSkelFlag.pattern;
                  if (CANONICAL_SET.contains(pattern)) {
                      continue;
                  }
                  String trial = getBestPattern(cur.toString(), cur, MATCH_NO_OPTIONS);
                  if (trial.equals(pattern)) {
                      output.add(pattern);
                  }
              }
              ///CLOVER:OFF
              //The following would never be called since the parameter is false
              //Eclipse stated the following is "dead code"
              /*if (false) { // ordered
                  DateTimePatternGenerator results = new DateTimePatternGenerator();
                  PatternInfo pinfo = new PatternInfo();
                  for (DateTimeMatcher cur : skeleton2pattern.keySet()) {
                      String pattern = skeleton2pattern.get(cur);
                      if (CANONICAL_SET.contains(pattern)) {
                          continue;
                      }
                      //skipMatcher = current;
                      String trial = results.getBestPattern(cur.toString());
                      if (trial.equals(pattern)) {
                          output.add(pattern);
                      } else {
                          results.addPattern(pattern, false, pinfo);
                      }
                  }
              }*/
              ///CLOVER:ON
              return output;
          }
      }
docs: Redundant patterns are those which if removed, make no difference in the
  resulting getBestPattern values. This method returns a list of them, to
  help check the consistency of the patterns used to build this generator.
  
  @param output stores the redundant patterns that are removed. To get these
  in internal order, supply a LinkedHashSet. If null, a
  collection is allocated.
  @return the collection with added elements.
  @deprecated This API is ICU internal only.
  @hide original deprecated declaration
  @hide draft / provisional / internal are hidden on Android