### Question:
RMap extends RCollection { @Override public boolean isExist(String key) throws KitDBException { try (CloseLock ignored = checkClose()) { byte[] key_b = getKey(key); byte[] k_v = getDB(key_b, SstColumnFamily.META); Meta meta = addCheck(key_b, k_v); return meta != null; } } protected  RMap(DB db); void put(String key, String mkey, byte[] value); void putTTL(String key, String mkey, byte[] value, int ttl); void put(String key, Map<String, byte[]> map); void putMayTTL(String key, int ttl, Map<String, byte[]> map); void putMayTTL(String key, int ttl, String mkey, byte[] value); Map<String, byte[]> get(String key, String... keys); byte[] get(String key, String mkey); void remove(String key, String... keys); @Override void delete(String key); @Override KeyIterator getKeyIterator(); void deleteFast(String key); @Override RIterator<RMap> iterator(String key); @Override Entry getEntry(RocksIterator iterator); @Override int getTtl(String key); @Override void delTtl(String key); @Override void ttl(String key, int ttl); @Override boolean isExist(String key); @Override int size(String key); static byte[] HEAD_B; final static byte[] HEAD_KEY_B; }### Answer:
@Test public void isExist() throws Exception { String head = "isExist0"; RMap map = db.getMap(); int num = 1000; try { for (int i = 0; i < num; i++) { map.put(head, "hello" + i, ("world" + i).getBytes()); } Assert.assertTrue(map.isExist(head)); map.ttl(head, 3); Assert.assertTrue(map.isExist(head)); Thread.sleep(3000); Assert.assertTrue(!map.isExist(head)); for (int i = 0; i < num; i++) { map.put(head, "hello" + i, ("world" + i).getBytes()); } Assert.assertTrue(map.isExist(head)); map.deleteFast(head); Assert.assertTrue(!map.isExist(head)); } finally { map.delete(head); } }