buffered writer vs. sys out print

问题

I am pretty new to java and wanted to understand the reasoning why this does not work. Why does the sys out print work perfectly, but the buffered writer does not? I am just trying to understand the difference between the two/

//print the input matrix to the user

System.out.println("Matrix read: ");
System.out.println("------------------" +
                   "---------------------");
for (int i = 0; i < size; i++) {
    for (int j = 0; j < size; j++) {
        System.out.printf("%5d ", a[i][j]);
        bw.write(a[i][j]);
        bw.flush();
    }

    //print a blank line
    System.out.println();

buffered writer output (from .txt file):

     The Determinant is: 5
     The Determinant is: 3
     �The Determinant is: 64
�   ��  ���The Determinant is: 270
������   ���The Determinant is: 0
��������    ����The Determinant is: 270
������    The Determinant is: 0
    The Determinant is: 0

Sys out print output:

Matrix read: 
---------------------------------------
    5 
---------------------------------------
Matrix read: 
---------------------------------------
    2     3 
---------------------------------------
    5     9 
---------------------------------------
Matrix read: 
---------------------------------------
    3    -2     4 
---------------------------------------
   -1     5     2 
---------------------------------------
   -3     6     4 
---------------------------------------

回答1:

Instead of writing a raw int with

bw.write(a[i][j]);

(if you want the same thing written to your BufferedWriter) you need to format your output the same way. You could use String.format and something like

bw.write(String.format("%5d ", a[i][j]));

And, you'll need to add a new line (where you call System.out.println) if you want it to be identical, like

bw.write(System.lineSeparator());

回答2:

With write() you write bytes. In your first matrix you have the numerical value 5. If you use write(5), you write the byte value 5 which is a non-printable character that the text editor you are using is displaying somehow. If you use a hexdump utility, you will see that it acutally is the byte 5.

To the printf function you five a format string with which you tell it how to format the argument, which is the number 5. %5d here means format the number as string with at least 5 width, filled with spaces in front. and then a space afterwards.

If you want to have the same effect on your buffered writer, wrap it in a PrintWriter and use the same printf method and arugments and you will get the same result. If you only want to format the number as String in the BufferedWriter, you have to convert your number to a String befory you write it, e. g. with Integer.toString(5).getBytes() and then write this byte array with the according write() method.

回答3:

System.out is a PrintStream; to get the same behavior, try using a PrintStream (or PrintWriter) instantiated with your file name and use the print/println/format methods.

The BufferedWriter.write(int c) methods interprets the int parameter as a character, so if you pass 32, it's going to print a space character; that's most likely not what you want here.

来源：https://stackoverflow.com/questions/38416078/buffered-writer-vs-sys-out-print

标签

java

bufferedwriter