### Question:
RMap extends RCollection { @Override public void ttl(String key, int ttl) throws KitDBException { checkTxStart(); try (CloseLock ignored = checkClose()) { byte[] key_b = getKey(key); LockEntity lockEntity = lock(key); try { Meta metaV = getMeta(key_b); if (metaV == null) { metaV = new Meta(0, -1, db.versionSequence().incr()); } start(); delTimerCollection(KeyEnum.COLLECT_TIMER, metaV.getTimestamp(), key_b, metaV.convertMetaBytes().toBytesHead()); metaV.setTimestamp((int) (System.currentTimeMillis() / 1000 + ttl)); putDB(key_b, metaV.convertMetaBytes().toBytes(), SstColumnFamily.META); setTimerCollection(KeyEnum.COLLECT_TIMER, metaV.getTimestamp(), key_b, metaV.convertMetaBytes().toBytesHead()); commit(); } finally { unlock(lockEntity); release(); } checkTxCommit(); } catch (KitDBException e) { checkTxRollBack(); throw e; } } 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 ttl() throws Exception { String head = "ttl0"; RMap map = db.getMap(); int num = 1000; try { for (int i = 0; i < num; i++) { map.put(head, "hello" + i, ("world" + i).getBytes()); } map.ttl(head, 3); Thread.sleep(3500); for (int i = 0; i < num; i++) { byte[] bytes = map.get(head, ("hello" + i)); Assert.assertNull(bytes); } } finally { map.delete(head); } }