如何使用 Java 中的 BufferedReader 从文件中读取整数？

Question

我正在使用 Java 中的 BufferedReader，希望在读取整数方面得到一些指导。

总而言之，输入文件的每一行将代表无向图中的一条边。它将包含两个整数，即边的端点，后跟一个实数，即边的权重。最后一行将包含 -1，表示输入结束。

我已经创建了一个 BufferedReader 对象并初始化了一个整数变量和

文件格式如下：

 0   1    5.0
 1   2    5.0
 2   3    5.0
...
 5  10    6.0
 5  11    4.0
17  11    4.0
-1

public static void processFile(String inputFilePath) throws IOException {
        //Check to see if file input is valid
        if (inputFilePath == null || inputFilePath.trim().length() == 0) {
            throw new IllegalArgumentException("Error reading file.");
        }

        //Initialize required variables for processing the file
        int num = 0;
        int count = 0;

        try {
            //We are reading from the file, so we can use FileReader and InputStreamReader.
            BufferedReader fileReader = new BufferedReader(new FileReader(inputFilePath));
            //Read numbers from the line
            while ((num = fileReader.read()) != -1) { //Stop reading file when -1 is reached
                //First input is the start

                //Second input is the end
                //Third input is the weight



            }
        } catch (IOException e) {
            throw new IOException("Error processing the file.");
        }
    } 

这是我迄今为止所尝试的，但我想知道如何获取每一行代码，并将第一个数字作为“开始”变量，第二个数字作为“结束”变量，第三个数字是“重量”变量吗？我在网上看到了一些创建数组的解决方案，但由于我的文件格式，我有些困惑。我可以帮助澄清有关的任何细节

Answer 1

我会首先检查我是否可以读取文件（您可以使用File.canRead() 来做到这一点）。接下来，我将编译一个具有三个分组操作的正则表达式。然后我会使用BufferedReader.readLine() 来读取文本行； read() 调用返回单个字符。然后它只剩下解析匹配的行。而且我认为吞下原始异常只是为了重新抛出它没有任何意义（实际上，您会丢失当前的所有堆栈跟踪信息）。综上所述，

public static void processFile(String inputFilePath) throws IOException {
    File f = new File(inputFilePath);
    if (!f.canRead()) {
        throw new IllegalArgumentException("Error reading file.");
    }

    // Initialize required variables for processing the file
    try (BufferedReader fileReader = new BufferedReader(new FileReader(inputFilePath))) {
        Pattern p = Pattern.compile("^\\s*(\\d+)\\s+(\\d+)\\s+(\\d.+)$");
        String line;
        while ((line = fileReader.readLine()) != null) {
            Matcher m = p.matcher(line);
            if (m.matches()) {
                int start = Integer.parseInt(m.group(1));
                int end = Integer.parseInt(m.group(2));
                double weight = Double.parseDouble(m.group(3));
                System.out.printf("start=%d, end=%d, weight=%.2f%n", start, end, weight);
            }
        }
    }
}

Answer 2

切换到 readLine 并使用扫描仪：

public static void processFile(String inputFilePath) throws IOException {
    // Check to see if file input is valid
    if (inputFilePath == null || inputFilePath.trim()
                                              .length() == 0) {
        throw new IllegalArgumentException("Error reading file.");
    }

    // Initialize required variables for processing the file
    String line;
    int count = 0;

    // We are reading from the file, so we can use FileReader and InputStreamReader.
    try (BufferedReader fileReader = new BufferedReader(new FileReader(inputFilePath))) {

        // Read numbers from the line
        while ((line = fileReader.readLine()) != null) { // Stop reading file when -1 is reached
            Scanner scanner = new Scanner(line);

            // First input is the start
            int start = scanner.nextInt();

            if (start == -1) {
                break;
            }

            // Second input is the end
            int end = scanner.nextInt();

            // Third input is the weight
            double weight = scanner.nextDouble();

            // do stuff
        }
    } catch (IOException e) {
        throw new IOException("Error processing the file.");
    }
}

Answer 3

您可以使用readLine 而不是使用read，然后使用拆分，我认为您的分隔符是三个空格？

        try (BufferedReader fileReader = new BufferedReader(new FileReader(inputFilePath))) {
            String line;
            while(!(line = fileReader.readLine()).equals("-1")) {
                String[] edge = line.split("   ");
                int start = Integer.parseInt(edge[0]);
                int end = Integer.parseInt(edge[1]);
                double weight = Double.parseDouble(edge[2]);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }