CollectionUtil { public static String mkString(Collection<?> collection, String sep) { return mkString(collection, "", sep, ""); }  static String mkString(Collection<?> collection, String sep); static String mkString(Collection<T> collection, String start, String sep, String end); static boolean equalContentsIgnoreOrder(Collection<?> c1, Collection<?> c2); static Set<T> symmetricDifference(Collection<? extends T> c1, Collection<? extends T> c2); static Collection<T> filter(Collection<?> collection, Class<T> lowerBound); static T first(Collection<T> collection); static Optional<T> firstMatching(T[] array, Predicate<? super T> predicate);  }
@Test public void testMkString() { assertEquals("1, 2, 3, 4", CollectionUtil.mkString(Arrays.asList(1, 2, 3, 4), ", ")); }