java - 使用来自 Java 的扫描仪打印文件中的元素

Question

您好，我需要一些 Java 方面的帮助。因为我一直在尝试使用扫描仪从文件中输出行，但我没有成功。这是文件内容的样子:

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

我尝试做的第一件事是从第三行开始输出信息，而且效果非常好。这是代码:

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();
        }
    }

}

但是当我插入值 4 和(第一行和第二行)时，我试图弄清楚如何处理它。我做的第一件事是尝试使用 if 条件来查看分隔符是否存在，如果不存在，我将其打印出来:

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();
        }
    }

}

但它并没有像预期的那样工作，我将这个错误作为输出

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

拜托，我知道我可以处理它，但我一直在思考，但我不知道该怎么做。请帮忙谢谢。

Answer 1

我认为每一行的正则表达式 replaceAll 都可以做到这一点。

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

如果输入与模式匹配，则将其格式化为“x -> y costs z”，否则 replaceAll 将不执行任何操作并输出相同的行。

如果你想要这三个值，你可以使用 Matcher.group 访问捕获的值，

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);
    }
}