Screens and printers are output devices. Null by default. Aliasing is the process of drawing an object with jagged edges . Antialiasing is the process of removing those jagged edges. The rasterizer takes an object and determines how much of each pixel that object covers and produces a number to represent that coverage.
Lower numbers get less coverage as opposed to higher numbers.
This reduces the jaggedness and thus antialiases the image. User space is the space represented by Cartesian coordinates where Java 2D objects are drawn. When objects are drawn to a screen or printer User space is transformed to Device space. Usually one unit in device space corresponds to one pixel of a device. 72 user space coordinates to 1 physical inch.