Printing elements from a file using Scanner from Java

Question

Hello Please i need some help in Java. Since i have been trying to output lines from a file using Scanner but i dont succeed. This is how the file content looks like :

4
5
3->1->25
1->0->12
2->0->-5
0->1->0
2->1->7

The first thing i tried to do was to output information starting from the third line and it worked perfectly well. This is the code:

public static void main(String[] args) throws Exception {
    Scanner scanner = null;
    BufferedReader in = null;
    String line = null;
    try{
        scanner = new Scanner(new BufferedReader(new FileReader("graphe.txt")));
        //in = new BufferedReader(new FileReader("graphe.txt"));
        scanner.useDelimiter("->");
        while (scanner.hasNextLine()){

            int value = scanner.nextInt();
            scanner.skip(scanner.delimiter());
            int value2 = scanner.nextInt();
            scanner.skip(scanner.delimiter());
            String value3 = scanner.nextLine();
            int value3Int = Integer.parseInt(value3);
            System.out.println(value + " - > " + value2 + " cost " + value3Int);
        }

    }catch (IOException e){
        e.printStackTrace();
    }finally {
        if (scanner != null){
            scanner.close();
        }
    }

}

}

But then when i inserted values 4 and (first and second line) i tried to figure how to deal with it. The first thing i did was to try to use the if condition to see if the delimeter exist and if it doesn't i print it out :

public static void main(String[] args) throws Exception {
    Scanner scanner = null;
    BufferedReader in = null;
    String line = null;
    try{
        scanner = new Scanner(new BufferedReader(new FileReader("graphe.txt")));
        //in = new BufferedReader(new FileReader("graphe.txt"));
        scanner.useDelimiter("->");
        while (scanner.hasNextLine()){

            String find = scanner.nextLine();
            if (!(find.contains("->"))){
                System.out.println(find);
            }
            else {
                int value = scanner.nextInt();
                scanner.skip(scanner.delimiter());
                int value2 = scanner.nextInt();
                scanner.skip(scanner.delimiter());
                String value3 = scanner.nextLine();
                int value3Int = Integer.parseInt(value3);
                System.out.println(value + " - > " + value2 + " cost " + value3Int);
            }
        }

    }catch (IOException e){
        e.printStackTrace();
    }finally {
        if (scanner != null){
            scanner.close();
        }
    }

}

}

But it didn't work like expeceted and i had this error as output

4

5

Exception in thread "main" java.util.NoSuchElementException
    at java.base/java.util.Scanner.throwFor(Scanner.java:937)

1 - > 0 cost 12

    at java.base/java.util.Scanner.next(Scanner.java:1594)

0 - > 1 cost 0

    at java.base/java.util.Scanner.nextInt(Scanner.java:2258)
    at java.base/java.util.Scanner.nextInt(Scanner.java:2212)
    at com.tpTG.LectureGrapheMatrice.main(LectureGrapheMatrice.java:25)

Process finished with exit code 1

Please i know i can deal with it but i've been thinking over and over but i can't figure how to. Please help thanks.

Answer 1

I think a regex replaceAll for each line might do it.

// no need to set delimiter
while (scanner.hasNextLine()) {
    String line = scanner.nextLine().replaceAll("^((?:\\+|-)?\\d+)->((?:\\+|-)?\\d+)->((?:\\+|-)?\\d+)$", 
                                                "$1 -> $2 costs $3");
    System.out.println(line);
}

If the input matches the pattern, you format it to "x -> y costs z", otherwise replaceAll won't do anything and you output the same line.

If you want the three values, you can access the captured values with Matcher.group,

while (scanner.hasNextLine()) {
    String line = scanner.nextLine();
    Matcher m = Pattern.compile("((?:\\+|-)?\\d+)->((?:\\+|-)?\\d+)->((?:\\+|-)?\\d+)").matcher(line);
    if (m.matches()) {
        // m.group(1), m.group(2) and m.group(3) are the three values as strings. You can convert them to ints yourself.
        System.out.println(m.group(1) + " -> " + m.group(2) + " costs " + m.group(3));
    } else {
        System.out.println(line);
    }
}