Java program to merge two files into a third file

Prerequisite : PrintWriter , BufferedReader

Let the given two files be file1.txt and file2.txt. Our Task is to merge both files into third file say file3.txt. The following are steps to merge.

  1. Create PrintWriter object for file3.txt
  2. Open BufferedReader for file1.txt
  3. Run a loop to copy each line of file1.txt to file3.txt
  4. Open BufferedReader for file2.txt
  5. Run a loop to copy each line of file2.txt to file3.txt
  6. Flush PrintWriter stream and close resources.

To successfully run the below program file1.txt and file2.txt must exits in same folder OR provide full path for them.

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// Java program to merge two 
// files  into third file
  
import java.io.*;
  
public class FileMerge 
{
    public static void main(String[] args) throws IOException 
    {
        // PrintWriter object for file3.txt
        PrintWriter pw = new PrintWriter("file3.txt");
          
        // BufferedReader object for file1.txt
        BufferedReader br = new BufferedReader(new FileReader("file1.txt"));
          
        String line = br.readLine();
          
        // loop to copy each line of 
        // file1.txt to  file3.txt
        while (line != null)
        {
            pw.println(line);
            line = br.readLine();
        }
          
        br = new BufferedReader(new FileReader("file2.txt"));
          
        line = br.readLine();
          
        // loop to copy each line of 
        // file2.txt to  file3.txt
        while(line != null)
        {
            pw.println(line);
            line = br.readLine();
        }
          
        pw.flush();
          
        // closing resources
        br.close();
        pw.close();
          
        System.out.println("Merged file1.txt and file2.txt into file3.txt");
    }
}

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Output:

Merged file1.txt and file2.txt into file3.txt

Note : If file3.txt exist in cwd(current working directory) then it will be overwritten by above program otherwise new file will be created.

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