### Question:
StringUtils { public static String toString(Object obj) { if (obj == null) { return "null"; } if (obj.getClass().isPrimitive()) { return String.valueOf(obj); } if (obj instanceof String) { return (String)obj; } if (obj instanceof Number || obj instanceof Character || obj instanceof Boolean) { return String.valueOf(obj); } if (obj instanceof Date) { return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.S").format(obj); } if (obj instanceof Collection) { StringBuilder sb = new StringBuilder(); sb.append("["); if (!((Collection)obj).isEmpty()) { for (Object o : (Collection)obj) { sb.append(toString(o)).append(","); } sb.deleteCharAt(sb.length() - 1); } sb.append("]"); return sb.toString(); } if (obj instanceof Map) { StringBuilder sb = new StringBuilder(); sb.append("{"); if (!((Map)obj).isEmpty()) { for (Object k : ((Map)obj).keySet()) { Object v = ((Map)obj).get(k); sb.append(toString(k)).append("->").append(toString(v)).append(","); } sb.deleteCharAt(sb.length() - 1); } sb.append("}"); return sb.toString(); } StringBuilder sb = new StringBuilder(); Field[] fields = obj.getClass().getDeclaredFields(); for (Field field : fields) { field.setAccessible(true); sb.append(field.getName()); sb.append("="); try { Object f = field.get(obj); if (f.getClass() == obj.getClass()) { sb.append(f.toString()); } else { sb.append(toString(f)); } } catch (Exception e) { } sb.append(";"); } return sb.toString(); } private  StringUtils(); static boolean isNullOrEmpty(String str); static boolean isBlank(String str); static boolean isNotBlank(String str); static boolean equals(String a, String b); static boolean equalsIgnoreCase(String a, String b); static String inputStream2String(InputStream is); static byte[] inputStream2Bytes(InputStream is); static String toString(Object obj); static String trimToNull(final String str); static String trim(final String str); static boolean isEmpty(final CharSequence cs); static boolean isNotEmpty(final CharSequence cs); static final String EMPTY; }### Answer:
@Test void testCycleDependency() { CycleDependency A = CycleDependency.A; try { StringUtils.toString(A); } catch (StackOverflowError e) { Assertions.fail("stack overflow error"); } }