基于Java的画图程序源代码，定义图案类型，记录鼠标拖动的起始点和终点、增加鼠标事件、鼠标释放事件、重绘屏幕、根据shape值绘制图形(Java-based drawing program source code, define the pattern type, record the starting point and end point of the mouse drag, add mouse events, mouse release events, redraw the screen, draw graphics according to the shape value)