实现图形交互工具：把交互图形操作功能抽象出来，设计一个工具类层次，实现了初步的图形交互绘制功能。-interactive graphics tools : put interactive feature abstract graphics, and design a class hierarchy tool, achieving a preliminary mapping of interactive graphics functions.

基本的绘图程序，有直线，圆等基本图形， 精髓在于类的层次设计，是很好的面向对象初学实例-basic mapping procedures, straight lines, circles and other basic graphics category essence is the level design, is a good example of the object-oriented learning