Stepping through a text file line by line

I'm attempting to write a program that steps through lines from a text file (to be used in conjunction with MaxMsp. I'd like to read a whole text file and output a single line, then trigger the output of the next line.

I'm not sure if there is a way to tokenize the lines, and recall them later. Or perhaps I should read them into an array and display the arrays.

I appreciate any help that can be offered.

The problem with reading in the entire file all at once is you can run out of memory if it is a large file. Much easier is to use a Scanner to read the file line by line.

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I'm attempting to write a program that steps through lines from a text file

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Create a buffered reader and repeatedly call its readLine() method. Java Developers ALmanac have an example.

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I'd like to read a whole text file and output a single line, then trigger the output of the next line.

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Why? I ask because this is a rather different aim from that expressed above. If you go this route you would read the entire textual content (and hope that it's not too large) and then tokenise the resulting String as you suggest. The String split() method will give you an array of lines - but knowing what to use as the regex argument will depend on the format of the text file (and possibly what you intend doing with empty lines etc)

[Edit] Or you could create a list of strings and populate it with readLine() as described above.

Here is a file I wrote that reads a text file line by line.

Code:

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

public class IOPractice
{
        public static void main(String[] args) throws IOException
        {
                Scanner s = new Scanner(System.in);
               
                File f = new File("file.txt");
                Scanner numScan = new Scanner(f);
               
                String line;
               
                while (numScan.hasNext())
                {
                        line = numScan.nextLine();
                        System.out.print(line + " ");
                }
               
               
        }
}

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In line

Code:

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File f = new File("file.txt");

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you'll want to enter the filename of a text file in the same folder.

Hope that helps.

pbrockway2,

I'm trying to send each line from a text file (a book) out to be processes by another programming environment. I don't care too much how this happens inside of java, but I'd like it to happen.

I don't understand how to call the readline() from a buffered reader, but this sounds like a good approach.

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I don't understand how to call the readline() from a buffered reader, but this sounds like a good approach.

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Did you try (and understand) the Almanac example? It does exactly what you are describing.

I did try, unfortunately my skill with java are so weak I was unable to understand the code. Right now my non-working model is as basic as this

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class Reader {

void readLine(String fileName)
{
java.io.BufferedReader br = null;
try {
BufferedReader in = new BufferedReader(new FileReader("/users/evanlivingston/Desktop/Text.txt"));
String str;
while ((str = in.readLine()) != null) {
System.out.println(str);
}
in.close();
} catch (IOException e) {
}
}
}

A StringBuffer is not required. If you are just displaying it, import the Scanner class and create an instance of it. A simple while loop will iterate through the entire contents of the text file. Just make sure the text file is in the same directory as the java file.

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Right now my non-working model is as basic as this

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So what happens when you compile and run the code?

Also, if you don't understand the example, or aren't familiar with the overall structure of a Java program with its main() method and so on, perhaps you should start with the basics: a book, or Oracle's Tutorial. I don't say this to be discouraging but, rather, becuase I believe it's the fastest way to make progress.

When I compile the program displays the entire contents of a text file. I'm not sure how to specify to read just one line. I don't understand how to modify the readline() nor can I find examples doing this.

Thanks again.

(I'm working through tutorials, unfortunately I'm only now learning how to add variables and print the output) I'm having a hard time find tutorials or books which discuss the most basic elements of java.

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When I compile the program displays the entire contents of a text file.

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The code you last posted doesn't do this because it doesn't run. (it lacks a main() method)

Post the code that displays the entire contents when run.