Remove Duplicate Lines in Java: Explanation & Practice

Problem summary

Read a file and write only unique lines to output.

Starter code

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

public class Main {
    public static void main(String[] args) {
        // Remove duplicate lines
        // Print: Removed <count> duplicates
    }
}

Expected output and test cases

• 3 duplicates found

  Removed 3 duplicates

• All unique

  Removed 0 duplicates

• Many duplicates

  Removed 5 duplicates

Hints

1. Use LinkedHashSet to maintain order
2. Set automatically removes duplicates
3. Count original - final size

Related File I/O exercises

• Practice Reverse File Lines in Java
• Practice Merge Multiple Files in Java
• Practice Sort File Lines in Java

Practice all File I/O exercises · Run this idea in the Java compiler