高手帮忙看看这个是什么问题?谢谢!
import *;
public class AA
{
    public static void main (String args[]) //throws IOException
    {
        String s[] = {"aaa\n","bbb\n","ccc\n"};
        try
        {
            RandomAccessFile rf = new RandomAccessFile ("AA.txt","rw");
            System.out.println (rf.getFilePointer ());
            System.out.println (rf.length());
            rf.seek (rf.length);
            for (int i=0; i < 3; ++i)
            {
                rf.writeBytes (s[i]);
            }
            rf.seek (0);
            String st;
            while ((st=rf.readLine()) != nul)
            {
                System.out.println (st);
            }
            rf.close ();
        }
        catch (FileNotFoundException e)
        {

        }
        catch (IOException g)
        {
        }
    }
}

---------- ￎ ----------
error: error reading c:\jdk1.5.0\lib\ir.idl; java.util.zip.ZipException: error in opening zip file
AA.java:12: cannot find symbol
symbol  : variable length
location: class
            rf.seek (rf.length);
                                   ^
AA.java:19: cannot find symbol
symbol  : variable nul
location: class AA
            while ((st=rf.readLine()) != nul)
                                                     ^
3 errors

输出完成 (耗时: 0 秒)