### Question:
StringUtils { public static Set<String> strToSet(String str, String delimiter) { return new LinkedHashSet<>(strToList(str, delimiter)); }  static boolean isEmpty(String str); static boolean isSameStr(String a, String b); static String setToStr(Set<String> stringSet, String delimiter); static String setToStr(Set<String> stringSet, String delimiter, String defaultRet); static Set<String> strToSet(String str, String delimiter); static List<String> strToList(String str, String delimiter); static boolean startWithToLowerCase(String thisString, String anotherString); static final String EMPTY_STRING; static final int CHAR_A; static final int CHAR_Z; static final int CASE_GAP; }### Answer:
@Test public void testStrToSet() { Set<String> set = StringUtils.strToSet(null, "&&"); Assert.assertTrue(set.isEmpty()); set = StringUtils.strToSet("ab&&ba&&cb&&cb", "&&"); Assert.assertTrue(set.size() == 3); Object[] array = set.toArray(); Assert.assertTrue(array[0].equals("ab")); Assert.assertTrue(array[1].equals("ba")); Assert.assertTrue(array[2].equals("cb")); }