我测试了上面的方法来计数行，这里是我对不同方法的观察，在我的系统上进行了测试

文件大小:1.6 Gb 方法:

使用扫描仪:大约35秒 使用BufferedReader:大约5s 使用Java 8: 5s左右 使用LineNumberReader:大约5s

此外，Java8方法似乎非常方便:

Files.lines(Paths.get(filePath), Charset.defaultCharset()).count()
[Return type : long]

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。

EOF处没有换行符('\n')的多行文件的最佳优化代码。

/**
 * 
 * @param filename
 * @return
 * @throws IOException
 */
public static int countLines(String filename) throws IOException {
    int count = 0;
    boolean empty = true;
    FileInputStream fis = null;
    InputStream is = null;
    try {
        fis = new FileInputStream(filename);
        is = new BufferedInputStream(fis);
        byte[] c = new byte[1024];
        int readChars = 0;
        boolean isLine = false;
        while ((readChars = is.read(c)) != -1) {
            empty = false;
            for (int i = 0; i < readChars; ++i) {
                if ( c[i] == '\n' ) {
                    isLine = false;
                    ++count;
                }else if(!isLine && c[i] != '\n' && c[i] != '\r'){   //Case to handle line count where no New Line character present at EOF
                    isLine = true;
                }
            }
        }
        if(isLine){
            ++count;
        }
    }catch(IOException e){
        e.printStackTrace();
    }finally {
        if(is != null){
            is.close();    
        }
        if(fis != null){
            fis.close();    
        }
    }
    LOG.info("count: "+count);
    return (count == 0 && !empty) ? 1 : count;
}

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();
    }
}

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);
    }

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。