Speeding up IO

Hi,
I have to work on file which are in GB's. They contain some id's and
their related data. These Id's repeat after few hundred or more lines
but with different data. I want to find these Id's and operate on the
data i.e for each id i want to compare data with similar id down the
file.
For this i'm writting following code...

class Risk
{
  static String file;
  String str,id,sid="0",eid,s,s1,s2,str1,str2,tok1,tok2;
  int
a,i=0,j=0,k,l,sc,line,no,flag=0,flag1=1,flag2=1,start=0,end=0,x,y,cnt;
  double
val1=0.0,val2=0.0,val3=0.0,val4=0.0,val5=0.0,val6=0.0,val7=0.0,val8=0.0,val9=0.0,val10=0.0;
  FileReader fr,fr1,fr2;
  BufferedReader br,br1,br2;
  FileWriter fw,fw1,fw2;
  StringTokenizer st;
  int[] subcase=new int{1,2,3,4};
  Vector qid=new Vector();
  qid.add(100);
  qid.add(101);
 qid.add(102);
 qid.add(103);
 qid.add(104);

  double qmax[]=new double[11];
  String[][] quad=new String[50][30];

  public void compare(String infile) throws IOException
  {
    cnt=0;
    for(i=0;i<qid.size();i++)
    {
      no=0;
      fr=new FileReader(infile);
      br=new BufferedReader(fr);
      while((str=br.readLine())!=null)
      {
        no++;
        if((str.startsWith("$"))||(str.startsWith("-CONT-")))
           continue;
        else
        {
          s2=str.substring(0,10);
          if(s2.equals(qid.elementAt(i)))
          {
            cnt++;
            start=no;
            end=no+29;
            quadarray(infile,start,end);
          }
          if((cnt==sc) && (i><qid.size()))
          {
             System.out.println("qid="+qid.elementAt(i));
             cnt=0;
             writesubcase1();
          }
       }
    }
    fr.close();
 }

  public void quadarray(String ifile,int start,int end) throws
IOException
  {
    try
    {
      fr1=new FileReader(ifile);
      br1=new BufferedReader(fr1);
      line=0;
      k=0;
      x=0;
      while((str1=br1.readLine())!=null)
      {
        line++;
        if((line>=start) && (line<end))
        {
           if(j==0)
          quad[j][k]=str1;
          if((k==3) || (k==17) || (k= ))
          {
             val1=Double.parseDouble(str1.substring(18,36));
             if(val1>qmax[x])
             {
               qmax[x]=val1;
               x++;
              }
           }
           if((k==5) || (k==8) || (k==22) || (k==25))
           {
             val2=Double.parseDouble(str1.substring(54,72));
             if(val2>qmax[x])
             {
                qmax[x]=val2;
                 x++;
             }
           }
           if((k==11) || (k==14) || (k==28))
           {
             val3=Double.parseDouble(str1.substring(36,54));
             if(val3>qmax[x])
             {
               qmax[x]=val3;
                x++;
             }
           }
            k++;
        }
      }
     }
    catch (Exception e)
    { }
  }

  public void writesubcase1() throws IOException
  {
    x=0;
    try
    {
       fw=new FileWriter("Result.txt",true);
       for(y=0;y<30;y++)
       {
          if((y==0) || (y==1) || (y==2) || (y==4) || (y==6) || (y==7)
|| (y==9) || (y==10) || (y==12) || (y==13) || (y==15) || (y==16) ||
(y==18) || (y==19) || (y==21) || (y==23) || (y==24) || (y==26) ||
(y==27))
           {
              fw.write(quad[0][y]+"\n");
             continue;
           }
          else
          {
             if((y==3) || (y==17) || (y= ))
             {
                s=quad[0][y];
                fw.write(s.substring(0,28)+qmax[x]
+s.substring(37)+"\n");
                x++;
                continue;
             }
             if((y==5) || (y==8) || (y==22) || (y==25))
             {
                s=quad[0][y];
                fw.write(s.substring(0,64)+qmax[x]+"\n");
                x++;
                continue;
              }
              if((y==11) || (y==14))
              {
                 s=quad[0][y];
                 fw.write(s.substring(0,46)+qmax[x]
+s.substring(55)+"\n");
                 x++;
                 continue;
               }
               if(y==28)
               {
                  s=quad[0][y];
                  fw.write(s.substring(0,46)+qmax[x]+"\n");
                  x++;
                  break;
               }
            }
          }
          fw.close();
        }
        catch(Exception e)
         {}
   }

   public static void main(String []args)
   {
     Risk r=new Risk();
     file=args[0];
     r.compare();
   }

Can you tell me how can i speed up IO coz its really taking hell lot
of time to process data.

Thankx in advance.>