Question

Here I wrote Java code to display duplicate numbers in a text file. Here I hardcoded the path name of text file. I assumed that text file contains only numbers in every line of text file.

And I like to display only those numbers which are repeated. Code is as shown below:

import java.util.*;
import java.io.*;

public class FileRead {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    HashMap<String,String> lines=new HashMap<String,String>();

    try{
        FileInputStream fstream=new FileInputStream("C:/Users/kiran/Desktop/text.txt");
        DataInputStream in=new DataInputStream(fstream);
        BufferedReader br=new BufferedReader(new InputStreamReader(in));
        ArrayList arr=new ArrayList();
        String str,str1;
        int i=0;
        while((str=br.readLine())!=null){
            i++;
            str1=Integer.toString(i);
            if(lines.containsValue(str)){
                System.out.println(str);
            }else{
                lines.put(str1, str);
            }
        }
        in.close();
    }catch(Exception e){
        System.out.println(e);
    }

}
}

Contents of text file is as shown below:

 56
 75
 1
 46
 100
 97
 75
 46
 46

Expected output is:

 75
 46

This is the output I’m getting:

 75
 46
 46

I’m not able to find out the error in the program. Can anyone help me??

Answer 1

You needed to keep track of what you have printed, for example in a HashSet<String>.

Declare Set<String> seen = new HashSet<String>() at the top, then add an if:

if(lines.containsValue(str)){
    if (seen.add(str)) {
        System.out.println(str);
    }
} else {
    lines.put(str1, str);
}

An even easier solution is to remove else:

if(lines.containsValue(str)){
    System.out.println(str);
}
lines.put(str1, str);