FileInputStream如何读取工作？

Question

Someone please explain me how buffer array is filled in the following code:

try {
        byte[] buffer = new byte[1024];
        //(1) this print an empty string?
        System.out.println("1: " + new String(buffer));
        FileInputStream inputStream = new FileInputStream("test.txt");
        int len;

        while((len = inputStream.read(buffer)) != -1) {
            //(2) this print text on my file?
            System.out.println("2: " + new String(buffer));
        }
        inputStream.close();

    } catch (IOException e) {
        e.printStackTrace();
    }

Update : i have got useful info after reading following: https://docs.oracle.com/javase/tutorial/essential/io/bytestreams.html

Buffered input streams read data from a memory area known as a buffer; the native input API is called only when the buffer is empty. Similarly, buffered output streams write data to a buffer, and the native output API is called only when the buffer is full

Thanks all!

Answer 1

The InputStream#read method will read data from the input stream into the supplied buffer.

See the java doc for details.

(In particular, see the return value – it will return -1 if there is no more data to read.)