JDK的drawRect()，实际绘制范围比宽度大一个像素

package taishan;
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
@SuppressWarnings("serial")
public class DrawRectFrame extends TFrame
{
  public DrawRectFrame()
  {
     this.getContentPane().setBackground(Color.WHITE);
     this.getContentPane().setLayout(null);
     setUndecorated(true);
  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE );
  }
  @Override
    public void paint(Graphics g)
    {
  super.paint(g);
  g.setColor(Color.RED);
  g.drawLine(0, 0, 20,  0);
  g.drawLine(0, 0,  0, 20);
  g.setColor(Color.BLUE);
  g.drawRect(5, 5, 10, 10);
    }
  public static void main(String[] args)
    {
  DrawRectFrame frame = new DrawRectFrame();
  frame.setSize(600, 400);
  frame.setLocation(100, 100);
  frame.setVisible(true);
    }
}