Coordinates

You are probably familiar with Cartesian coordinates in two dimensions, in which each location is identified by an x-coordinate (distance along the x-axis) and a y-coordinate. By convention, Cartesian coordinates increase to the right and up, as shown in the figure.

Annoyingly, it is conventional for computer graphics systems to use a variation on Cartesian coordinates in which the origin is in the upper-left corner of the screen or window, and the direction of the positive y-axis is down. Java follows this convention.

The unit of measure is called a pixel; a typical screen is about 1000 pixels wide. Coordinates are always integers. If you want to use a floating-point value as a coordinate, you have to round it off to an integer (See Section 3.2).