JAVA show the duplicate certain values in a text file

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;

public class pring
{
    private static ArrayList<String> data = new ArrayList<String>();
    public static void main(String[] args) throws IOException
    {
        arrayListConstructor("C:/Users/DfroJaCk DB/Desktop/zongrecv.txt");
        System.out.println(data);
    }
    public static void arrayListConstructor(String filename) throws IOException
    {
        HashMap<String, String> map = new HashMap<String, String>();

        BufferedReader br = null;
        br = new BufferedReader(new FileReader(filename));
        String line = br.readLine();
        while (line != null)
        {
            /* if line is new key, return null,
             * if line is duplicate key, return value
             */
            if (map.get(line) == null) {
                System.out.println("new: " + line);
                data.add(line);
                map.put(line, line);
            }
            else
                System.out.println("duplicate: " + line);

            line = br.readLine();
        }
        br.close();
    }
}