This .NET class wraps the AcDbLine ObjectARX class. 

This class represents the line entity in AutoCAD. A line object is a 3D object that is specified by its start point, endpoint, and normal vector. In addition, the line object supports thickness along its normal vector direction (that is, height or "extrusion").

Autodesk.AutoCAD.DatabaseServices.DBObject
    Autodesk.AutoCAD.DatabaseServices.Entity
        Autodesk.AutoCAD.DatabaseServices.Curve
            Autodesk.AutoCAD.DatabaseServices.Line

Public Class Line
Inherits Curve

public class Line : Curve;

DBObject, Entity, Point3d, Vector3d