groupby functionality in java

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
class Groupby{
    BufferedReader readexistingfile = null;
    String oldfileline;
    BufferedWriter writenewline = null;
    BufferedReader readnewfile = null;
    ArrayList<String> stringList = new ArrayList<String>();
    public void duplicate(String filename) {
        try {
        readexistingfile = new BufferedReader(new FileReader(filename));
        while((oldfileline = readexistingfile.readLine()) != null){
            //System.out.println("?????????"+oldfileline);
            //ArrayList<Integer> arry[] = oldfileline.split(",");
            newfile(oldfileline);
        }
        }catch(FileNotFoundException fnot){}
        catch(IOException io){}
        finally{
            try {                
                if(readexistingfile != null)readexistingfile.close();               
            } catch (IOException ex) {
                ex.printStackTrace();
            }   
        }
    }
    public void newfile(String line) {
        //System.out.println("------"+line);
        try {
        // boolean flag = false;
        writenewline = new BufferedWriter(new FileWriter("d://groupfile.txt"));
        //readnewfile = new BufferedReader(new FileReader("d://groupfile.txt"));

        stringList.add(line);

         for(int i=0;i<stringList.size();i++) {
                    //System.out.println("loop"+stringList.size());
               if(!(stringList.get(i).equals(line))) {
                    System.out.println("equals"+line);
                     writenewline.write(line);
                     writenewline.newLine();
                     writenewline.flush();  
                    }
               else{
                   break;
               }
               }         
        } catch(IOException io){}
    }
    public static void main(String arg[]){
        Groupby group = new Groupby();
        group.duplicate("d://raju.txt");        
    }
}