如果你用这个

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;
}

你不能运行到大num行，比如100K行，因为从读取器返回。getLineNumber是int。你需要长类型的数据来处理最多的行。

似乎有几种不同的方法可以使用LineNumberReader。

我是这样做的:

int lines = 0;

FileReader input = new FileReader(fileLocation);
LineNumberReader count = new LineNumberReader(input);

String line = count.readLine();

if(count.ready())
{
    while(line != null) {
        lines = count.getLineNumber();
        line = count.readLine();
    }
    
    lines+=1;
}
    
count.close();

System.out.println(lines);

更简单的是，可以使用Java BufferedReader lines()方法返回元素流，然后使用stream count()方法对所有元素进行计数。然后只需在输出中添加1，就可以得到文本文件中的行数。

为例:

FileReader input = new FileReader(fileLocation);
LineNumberReader count = new LineNumberReader(input);

int lines = (int)count.lines().count() + 1;
    
count.close();

System.out.println(lines);

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
}

这个有趣的解决方案真的很好!

public static int countLines(File input) throws IOException {
    try (InputStream is = new FileInputStream(input)) {
        int count = 1;
        for (int aChar = 0; aChar != -1;aChar = is.read())
            count += aChar == '\n' ? 1 : 0;
        return count;
    }
}

在java-8中，你可以使用流:

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

从Java代码中使用Process类如何?然后读取命令的输出。

Process p = Runtime.getRuntime().exec("wc -l " + yourfilename);
p.waitFor();

BufferedReader b = new BufferedReader(new InputStreamReader(p.getInputStream()));
String line = "";
int lineCount = 0;
while ((line = b.readLine()) != null) {
    System.out.println(line);
    lineCount = Integer.parseInt(line);
}

不过需要尝试一下。将公布结果。