Java Scanner Class Help

Question

I would like to find out how to print a a certain string from an input file using a scanner. For the string to be printed the line must start with *star and the string must be surrounded by quotation marks, and be the next token and on the same line as *star ignoring white space of course.

Sample input text file: "test.txt"

this is a test

*star "variableX"

more testing

*star "variableY

much more

testing

*star next"variableZ"

Based on this sample input text the output should be only.

"variableX"

Here is part of my code:

    Scanner scanner = new Scanner (new File ("test.txt"));

    while (scanner.hasNextLine()){

        if(scanner.hasNext("*star")) {
            scanner.next();

            if(scanner.hasNext()){
                String test = scanner.next();
                System.out.println(test);
            }

But it's missing some key things. Help is much appreciated!

Answer 1

This does the trick

public static void main(String[] args) throws FileNotFoundException
    {
        Scanner scanner = new Scanner (new File ("c:\\test.txt"));

        while (scanner.hasNextLine()){
            if(scanner.hasNext(Pattern.compile("\\*star"))) {
                scanner.next();
                System.out.println(scanner.nextLine());
                return;
            }
            else
                scanner.nextLine();
        }
    }

Edit: The quotation part was missing in the answer, did not remember to put it as I got the output even without it, but here it is a more robust solution:

Scanner scanner = new Scanner (new File ("c:\\new.txt"));

        while (scanner.hasNextLine()){
            if(scanner.hasNext(Pattern.compile("\\*star"))) {
                scanner.next();
                String s = scanner.nextLine();
                Matcher m = Pattern.compile("\".+\"").matcher(s);
                if(m.find())
                {
                    System.out.println(m.group());
                    return;
                }
            }
            else
                scanner.nextLine();
        }

Answer 2

package so3947761;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Main {
  private static final Pattern RELEVANT_LINE_PATTERN =
      Pattern.compile("^\\*star\\s+\"(.*)\"$");

  public static void main(String[] args) throws FileNotFoundException {
    Scanner scanner = new Scanner(new File("test.txt"));

    while (scanner.hasNextLine()) {
      String line = scanner.nextLine();

      Matcher m = RELEVANT_LINE_PATTERN.matcher(line);
      if (m.matches()) {
        String data = m.group(1);

        System.out.println(data);
      }
    }
  }
}

Some remarks:

• I'm using the Scanner only for splitting the input into lines.
• The real work is done by the regular expression pattern, which contains all the requirements that you stated.
• If you want to parse the text in quotes further (for example to replace \n with a newline), this cannot be done by the regular expression, so you have to explicitly define which sequences to replace.
• You may want to add \\s* at the right of the ^ (beginning of the line) and at the left of the $ (end of the line) if you want to allow whitespace at these places.