答案，Graphics

import java.awt.*;import java.awt.event.*;public class DrawLine extends Frame{    public DrawLine()    {        addWindowListener(new WindowAdapter()        {            public void windowClosing(WindowEvent e)            {                dispose();                System.exit(0);            }        });        this.addMouseListener(new MouseAdapter()        {            int orgX;            int orgY;            public void mousePressed(MouseEvent e)            {                orgX=e.getX();                orgY=e.getY();            }            public void mouseReleased(MouseEvent e)            {                Graphics g=getGraphics();//为什么等号右边要这么写。                g.setColor(Color.RED);                g.setFont(new Font(null,Font.ITALIC|Font.BOLD,30));                //g.setFont(Font.BOLD)为什么此处这么写会报错？为什么不能这么写？                g.drawString(orgX+","+orgY,orgX,orgY);                g.drawString(e.getX()+","+e.getY(),e.getX(),e.getY());                g.drawLine(orgX,orgY,e.getX(),e.getY());            }        });    }    public static void main(String []args)    {        DrawLine dl=new DrawLine();        dl.setSize(400,400);        dl.setTitle("窗体");        dl.setVisible(true);    }}