eclipse不能自动构建class文件

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环境配置

JDK1.5+Eclipse 3.1.1

文件源代码

package cimage;import java.io.*;import javax.servlet.http.*;import javax.servlet.*;import java.util.*;import java.awt.*;import java.awt.image.*;import javax.imageio.*;//import com.sun.image.codec.jpeg.*;public class Cimage extends HttpServlet{        /** *  */private static final long serialVersionUID = -6836950231563427102L;public void init(ServletConfig conf) throws ServletException        {                super.init(conf);        }                public void doGet(HttpServletRequest req,HttpServletResponse res) throws ServletException, IOException        {                res.setContentType("image/jpeg");                res.setHeader("Pragma","No-cache");                res.setHeader("Cache-Control","no-cache");                res.setDateHeader("Expires", 0);                HttpSession session = req.getSession();                                String chose="0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";                char display[]={'0',' ','0',' ','0',' ','0'},ran[]={'0','0','0','0'},temp;                // 在内存中创建图象                int width=60, height=20;                BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);                                // 获取图形上下文                Graphics g = image.getGraphics();                                // 生成随机类                Random random = new Random();                                // 设定背景色                g.setColor(getRandColor(200,250));                g.fillRect(0, 0, width, height);                                // 设定字体                g.setFont(new Font("Times New Roman",Font.PLAIN,18));                                // 画边框                //g.setColor(new Color());                //g.drawRect(0,0,width-1,height-1);                                // 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到                g.setColor(getRandColor(160,200));                for (int i=0;i<155;i++)                {                        int x = random.nextInt(width);                        int y = random.nextInt(height);                        int xl = random.nextInt(12);                        int yl = random.nextInt(12);                        g.drawLine(x,y,x+xl,y+yl);                }                                for (int i=0;i<4;i++)                {                 temp=chose.charAt(random.nextInt(chose.length()));                  display[i*2]=temp;                  ran[i]=temp;                  String randnum=String.valueOf(display[i*2]);                    g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));                        // 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成                    g.drawString(randnum,13*i+6,16);                }                                // 将认证码存入SESSION                                session.setAttribute("rand",String.valueOf(ran));                // 图象生效                g.dispose();                                // 输出图象到页面                ImageIO.write(image, "JPEG", res.getOutputStream());                //JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(res.getOutputStream());                //encoder.encode(image);        }                public void doPost(HttpServletRequest req,HttpServletResponse res) throws ServletException, IOException        {                doGet(req,res);        }                //给定范围获得随机颜色        private Color getRandColor(int fc,int bc)        {                Random random = new Random();                if(fc>255) fc=255;                if(bc>255) bc=255;                int r=fc+random.nextInt(bc-fc);                int g=fc+random.nextInt(bc-fc);                int b=fc+random.nextInt(bc-fc);                return new Color(r,g,b);    }}

出现的问题：

不知道是什么回事，关闭eclipse后，也不产生class文件，不知道哪位能不能告诉我？