code: @Override
      public void set(String key, Object value, int expiration) {
          Element element = new Element(key, value);
          if (expiration == 0) {
              element.setEternal(true);
          }
          element.setTimeToLive(expiration);
          cache.put(element);
      }
docs: Adds an entry in the cache.
  
  @param key        Item key.
  @param value      Item value.
  @param expiration Expiration time in seconds (0 second means eternity).