code: private void expungeExpiredEntries() {
          emptyQueue();
          if (lifetime == 0) {
              return;
          }
          int cnt = 0;
          long time = System.currentTimeMillis();
          for (Iterator<CacheEntry<K,V>> t = cacheMap.values().iterator();
                  t.hasNext(); ) {
              CacheEntry<K,V> entry = t.next();
              if (entry.isValid(time) == false) {
                  t.remove();
                  cnt++;
              }
          }
          if (DEBUG) {
              if (cnt != 0) {
                  System.out.println("Removed " + cnt
                          + " expired entries, remaining " + cacheMap.size());
              }
          }
      }
docs: Scan all entries and remove all expired ones.