static createLong(exchange, symbol, capital, options, adjustedPrice, clearCallback) {
    if (!(capital instanceof OrderCapital)) {
      throw new Error('TypeError: invalid OrderCapital');
    }

    const state = new PairState(exchange, symbol, PairState.STATE_LONG, options, adjustedPrice, clearCallback);
    state.capital = capital;
    return state;
  }
@param exchange String
@param symbol String
@param capital {OrderCapital}
@param options
@param adjustedPrice bool
@param clearCallback
@returns {PairState}