code: public double distance (Vector3 point) {
          double distance = -Float.MAX_VALUE;
          for (Plane plane : _planes) {
              distance = Math.max(distance, plane.distance(point));
          }
          return distance;
      }
docs: Determines the maximum signed distance of the point from the planes of the frustum. If
  the distance is less than or equal to zero, the point lies inside the frustum.