使用RandomAccessFile到达文件中的特定行 [英] Reaching a specific line in a file using RandomAccessFile

问题描述

是否可以通过RandomAccessFile将光标定位到文件中特定行的开头？

Is it possible to position cursor to the start of a specific line in a file through RandomAccessFile?

例如我想在文件中第111行的char 10到20之间更改String。该文件具有固定长度记录。

For e.g. I want to change String starting at char 10 till 20 in line 111 in a file. The file has fixed length records.

是否可以使用RandomAccessFile将光标直接定位到第111行的开头？

Is it possible to directly position the cursor to start of line 111 using RandomAccessFile ?

更新：

我使用了以下代码。但是，它返回null。

I used the following code. However, its returning null.

行长度为200个字符（如果我没有错，则为200字节）

Line length is 200 characters (which is 200 bytes if I am not wrong)

File f = new File(myFile); 
RandomAccessFile r = new RandomAccessFile(f,"rw"); 
r.skipBytes(200 * 99);   // linesize * (lineNum - 1) 
System.out.println(r.readLine());

我哪里错了？

推荐答案

我不确定但似乎RandomAccessFile不支持这样的功能。
由于RAF以字节运行，我们可以跳过特定的字节数，如果你的文件有固定的行宽，这可以通过

I'm not sure but seems RandomAccessFile do not support such functionality. As RAF operates with bytes we can skip specific amount of bytes, and if your file has fixed line width this can be achieved by

file.skipBytes(110 * lineSizeInBytes);

否则，你需要这样的东西：

Otherwise, you need something like this:

for (int i = 0; i < 110; i++) file.readLine();
String line = file.readLine();

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