Printing to the screen specific lines from a file

[stevenhaynes5]

Hi,

I have wrote this peice of code which takes 1 argument. The argument is a string and searches through a file and matches the string to a line in the file. For example

file.txt

Hello
1
3
4
END

with the arguemnt "Hello" the program should print from that line in the file until it finds the string "END". However i get the following error message.

bash-3.00$ java LogSearch "Hello"
Argument exists at line: 1
END exists at line: 5
Exception in thread "main" java.util.NoSuchElementException: No line found
        at java.util.Scanner.nextLine(Scanner.java:1471)
        at LogSearch.main(LogSearch.java:45)
bash-3.00$

Here is my code

/**
 *
 * @author steven.haynes
 */
import java.util.Scanner;
import java.io.File;
import java.io.FileNotFoundException;

public class LogSearch {

    public static void main(String[] args) throws FileNotFoundException {
        
        Scanner file = new Scanner(new File("file.txt"));
        
        int startLineNo = 0;
        int endLineNo = 0;
        String line = "";
        
        while (file.hasNext()) {
            
            line = file.nextLine();
            
            startLineNo++;
            
            if (line.equals(args[0])) {
                System.out.println("Argument exists at line: " + startLineNo);
                break;
            }
        }
        
        for (int j = startLineNo; file.hasNext(); j++) {
            
            line = file.nextLine();
            
            endLineNo++;
            
            if (line.equals("END")) {
                endLineNo = endLineNo + startLineNo;
                System.out.println("END exists at line: " + endLineNo);
                break;
            }
        }
        
        for (int i = startLineNo; i <= endLineNo; i++) {
            line = file.nextLine();
            System.out.println(line);
        }
        
        file.close();
    }
}

Can anyone help?

Thanks

[JosAH]

Why don't you test for file.hasNext() in your last for-loop?

kind regards,

Jos

[JosAH]

I hase the hasNext() methord to check if the file has anymore lines to read in it. Should this not be here? Please advise.

I'm sorry, I don't see that test anywhere in your last loop (just before you close the file).

kind regards,

Jos

[stevenhaynes5]

Sorry i did not ready your answer correctly. I can not see a way on implementing the hasNext() methord without changing whats inside the for loop. However if have changed it to

for (int count = 0; file.hasNext(); count++) {
            line = file.nextLine();
            if (count >= startLineNo && count <= endLineNo) {
                System.out.println(line);
            }

Unfortunaly this does not print the lines i want. It prints everything else but the lines i want.

Thanks,

[Norm]

It prints everything else but the lines i want.

Can you show the output that the program generates and also the contents of the file being read.

Do you expect the reading to restart at the beginning of the file after you have read through it once?

Try debugging your code by adding printlns to show the values of the variables as the change. You have a lot of integer variables that you set as you read the file. What are their values as the code executes?

[stevenhaynes5]

Ok basically the program gets a starting position. This is the line number of where args[0] matchs line x in file.txt. It then looks for END in file.txt and stores that line number. Having a starting position line 3 for example and an ending position line 10 for example i want to loop through file.txt only displaying lines 3 to 10. Is there an easier way to do this?

[Norm]

i want to loop through file.txt only displaying lines 3 to 10.

You need to start from the beginning again. Close the file and open it again to use the numbers you found.

Why read the file twice? Why not start displaying the lines when you find the start and stop displaying the lines when you find the end.
Or could the end be missing and you don't want to display anything unless you have found the end?

[stevenhaynes5]

Hi Norm,

This sounds good

Why read the file twice? Why not start displaying the lines when you find the start and stop displaying the lines when you find the end.

but i simply dontknow how to implement this.

[stevenhaynes5]

After a long hard think, i came up with the following solution.... And it works

import java.util.Scanner;
import java.io.File;
import java.io.IOException;

public class search {
    
    public static void main(String[] args) throws IOException {
        
        String line = null;
        String input = null;
        String exit = "END";
        
        input = args[0];
        
        Scanner file = new Scanner(new File("help_file"));
        
        while (file.hasNext()) {
            
            line = file.nextLine();
            
            if (line.contentEquals(input)) {
                
                do {
                    line = file.nextLine();
                    System.out.println(line);
                } while (!line.equals(exit));
            }
        }
    }
}

[Norm]

After a long hard think

Yes, that is how you have to do it sometimes. Some are easy, some are hard.