Reading a particular line from a text file in Java

Question

What is the most efficient way to extract specific line numbers of data from a text file? For example, if I use the Scanner to parse a file, do I first have to create an array with a length matching the total number of lines in the text file?

If a text file has 30 lines and I only want to work with lines 3, 8, and 12, is there a way to specifically only read those lines?

If you are not sure about the uniformity in length of each line , then loop using a counter probably ! — AllTooSir, Jul 25 '13 at 07:20
http://stackoverflow.com/questions/2312756/in-java-how-to-read-from-a-file-a-specific-line-given-the-line-number — Erik Pragt, Jul 25 '13 at 07:22
Awesome. Thanks everybody. I guess I'll be using the counter variable. Makes sense. — Jon, Jul 25 '13 at 07:29
@Jon, you should really accept one of the answers or write your answer — No Idea For Name, Sep 02 '13 at 06:32

No Idea For Name · Accepted Answer · 2013-07-25T07:53:02.000

here is how you do it:

import java.io.*;

public class Test {
public static void main(String [] args) {

    // The name of the file to open.
    String fileName = "temp.txt";
    int counter = 0;

    // This will reference one line at a time
    String line = null;
    FileReader fileReader = null;

    try {
        // FileReader reads text files in the default encoding.
        fileReader = 
            new FileReader(fileName);

        // Always wrap FileReader in BufferedReader.
        BufferedReader bufferedReader = 
            new BufferedReader(fileReader);

        while((line = bufferedReader.readLine()) != null) {
            counter++;
            if(counter == 3 || counter == 8 || counter == 12)
            {
               // do your code
            }
        }   

    }
    catch(FileNotFoundException ex) {
        System.out.println(
            "Unable to open file '" + 
            fileName + "'");                
    }
    catch(IOException ex) {
        System.out.println(
            "Error reading file '" 
            + fileName + "'");                  
        // Or we could just do this: 
        // ex.printStackTrace();
    }
    finally
    {
        if(fileReader != null){
           // Always close files.
           bufferedReader.close();            
        }
    }
}
}

You should be closing your streams in the `finally` block to ensure that an exception doesn't hold them open — MadProgrammer, Jul 25 '13 at 07:26
Now you have a reference issue ;) `bufferedReader` is defined within the context of the `try {...}` block which means it's not visible to the `finally` block...`close` also can throw an `IOException`. Yes, I'm making you work for that up-vote ;) — MadProgrammer, Jul 25 '13 at 07:39
@MadProgrammer that's why i hate fast edits... o well, i'll fix it — No Idea For Name, Jul 25 '13 at 07:51

score 3 · Answer 2 · answered Jul 25 '13 at 07:25

here is what you can do. (it is only part of your program, not exactly your program)

int counter 0 =;
BufferedReader br = new BufferedReader(new FileReader(file));  
String line;  
while ((line = br.readLine()) != null) {  
   // process the line.  
   counter++;

   switch(counter){  
    case 3:  
       \\ do your code for line no 3  
       break;  
    case 8:  
       \\ do your code for line no 8  
       break;  
    case 12:  
       \\ do your code for line no 12  
       break;  
   }  
}    
br.close();

newuser · Answer 3 · 2013-07-25T07:34:41.350

Try this

try
    {
        String sCurrentLine;
        br = new BufferedReader(new FileReader("File_Path"));
        int counter = 0;
        while ((sCurrentLine = br.readLine()) != null)
        {
            counter++;
            if (counter == 3 || counter == 8 || counter == 12)
            {
                System.out.println("" + br.read());
                if (counter == 12)
                    break;
            }
        }
    }
    catch (IOException e)
    {
        System.out.println("Exception " + e);

    }
    finally
    {
      try
        {
           if (br != null)
           {
               br.close();
           }
        }
        catch (IOException ex)
        {
           ex.printStackTrace();
        }
     }

score 1 · Answer 4 · edited May 23 '17 at 12:14

1

Regarding the last question: According to this answer, Java 8 enables you to extract specific lines from a file. Examples are provided in that answer.

edited May 23 '17 at 12:14

Community

1
1

answered Apr 12 '16 at 19:29

João Matos

6,102
5
41
76

score 0 · Answer 5 · answered Oct 05 '17 at 14:30

here you can find the the solution for reading a file according to the line no. This site is the best It contain this code in all the programming languages. And I have given you the java code.

https://www.rosettacode.org/wiki/Read_a_specific_line_from_a_file#Java

Reading a particular line from a text file in Java

5 Answers5