graphics.drawRect()方法

drawRect方法的官方API文档描述

drawRect
public void drawRect(int x,
                     int y,
                     int width,
                     int height)
Draws the outline of the specified rectangle. The left and right edges of the rectangle are at x and x + width. The top and bottom edges are at y and y + height. The rectangle is drawn using the graphics context's current color.
Parameters:
x - the x coordinate of the rectangle to be drawn.
y - the y coordinate of the rectangle to be drawn.
width - the width of the rectangle to be drawn.
height - the height of the rectangle to be drawn.

width和height的描述是错误的。

实践告诉我们，width,height参数应该是右下角的点的坐标。