code: public static ECKey fromPrivateAndPrecalculatedPublic(byte[] priv, byte[] pub) {
          checkNotNull(priv);
          checkNotNull(pub);
          return new ECKey(new BigInteger(1, priv), CURVE.getCurve().decodePoint(pub));
      }
docs: Creates an ECKey that simply trusts the caller to ensure that point is really the result of multiplying the
  generator point by the private key. This is used to speed things up when you know you have the right values
  already. The compression state of the point will be preserved.