在java-8中，你可以使用流:

try (Stream<String> lines = Files.lines(path, Charset.defaultCharset())) {
  long numOfLines = lines.count();
  ...
}

一个直接的方式使用扫描器

static void lineCounter (String path) throws IOException {

        int lineCount = 0, commentsCount = 0;

        Scanner input = new Scanner(new File(path));
        while (input.hasNextLine()) {
            String data = input.nextLine();

            if (data.startsWith("//")) commentsCount++;

            lineCount++;
        }

        System.out.println("Line Count: " + lineCount + "\t Comments Count: " + commentsCount);
    }

我已经实现了这个问题的另一个解决方案，我发现它在计算行数时更有效:

try
(
   FileReader       input = new FileReader("input.txt");
   LineNumberReader count = new LineNumberReader(input);
)
{
   while (count.skip(Long.MAX_VALUE) > 0)
   {
      // Loop just in case the file is > Long.MAX_VALUE or skip() decides to not read the entire file
   }

   result = count.getLineNumber() + 1;                                    // +1 because line index starts at 0
}

上面的count()方法给出的答案是，如果文件末尾没有换行符，就会出现行数错误——它无法计算文件中的最后一行。

这个方法更适合我:

public int countLines(String filename) throws IOException {
    LineNumberReader reader  = new LineNumberReader(new FileReader(filename));
int cnt = 0;
String lineRead = "";
while ((lineRead = reader.readLine()) != null) {}

cnt = reader.getLineNumber(); 
reader.close();
return cnt;
}

接受的答案有一个错误关闭多行文件，不以换行符结束。一个没有换行符的单行文件将返回1，但是一个没有换行符的两行文件也将返回1。下面是解决这个问题的公认解决方案的实现。endsWithoutNewLine检查对于除最终读取外的所有内容都是浪费的，但与整个函数相比，应该是微不足道的时间。

public int count(String filename) throws IOException {
    InputStream is = new BufferedInputStream(new FileInputStream(filename));
    try {
        byte[] c = new byte[1024];
        int count = 0;
        int readChars = 0;
        boolean endsWithoutNewLine = false;
        while ((readChars = is.read(c)) != -1) {
            for (int i = 0; i < readChars; ++i) {
                if (c[i] == '\n')
                    ++count;
            }
            endsWithoutNewLine = (c[readChars - 1] != '\n');
        }
        if(endsWithoutNewLine) {
            ++count;
        } 
        return count;
    } finally {
        is.close();
    }
}

扫描与regex:

public int getLineCount() {
    Scanner fileScanner = null;
    int lineCount = 0;
    Pattern lineEndPattern = Pattern.compile("(?m)$");  
    try {
        fileScanner = new Scanner(new File(filename)).useDelimiter(lineEndPattern);
        while (fileScanner.hasNext()) {
            fileScanner.next();
            ++lineCount;
        }   
    }catch(FileNotFoundException e) {
        e.printStackTrace();
        return lineCount;
    }
    fileScanner.close();
    return lineCount;
}

还没记。