两次在txt文件上使用bufferedreader？

Question

i have to count the lines on a file but later in the code I also have to print what's in that file, but I can't use the reader twice it just says null. How can I work this out without creating a bunch of bufferedreader objects? thanks

Answer 1

1. Print and count at the same time?
2. Move the lines to an array then print them?
3. Make sure you've closed the file before reopening again?

Answer 2

Try closing the buffer, and then re-opening it again.

    BufferedReader bufferedReader = new BufferedReader(new FileReader("src/main/java/com/william/sandbox/stackoverflow/samples20160306/Demo.java"));
    String line = bufferedReader.readLine();
    int lineCount = 0;
    while(line != null){
        lineCount += 1;
        line = bufferedReader.readLine();
    }
    System.out.println("Line count is: " + lineCount);

    bufferedReader.close();
    bufferedReader = new BufferedReader(new FileReader("src/main/java/com/william/sandbox/stackoverflow/samples20160306/Demo.java"));

    line = bufferedReader.readLine();
    while(line != null){
        System.out.println(line);
        line = bufferedReader.readLine();
    }
}

Answer 3

You can use BufferedReader 's mark() and reset() methods to jump back to a specific position.

try (BufferedReader r = new BufferedReader(new FileReader("somefile.txt"))) {
    // marks this position for the next 10 characters read
    // after that the mark is lost
    r.mark(10);

    // do some reading

    // jump back to the mark
    r.reset();
}

Note that, BufferedReader supports marking but not all Reader s do. You can use markSupported() to check.