Объясните плиз

public class Solution {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
//        String file1 = reader.readLine();
//        String file2 = reader.readLine();

        FileInputStream inputStream1 = new FileInputStream("c:/javarush/data.txt");
        FileOutputStream outputStream2 = new FileOutputStream("c:/javarush/result.txt");

        if (inputStream1.available() > 0) {
            byte[] buffer = new byte[inputStream1.available()];
            sort(buffer);                                           //переворот массива
            int count = inputStream1.read(buffer);
            outputStream2.write(buffer, 0, count);
        }
        inputStream1.close();
        outputStream2.close();


    }
    public static void sort(byte[] massive) {
        for (int i = 0; i < massive.length / 2; i++) {
            byte tmp = massive[i];
            massive[i] = massive[massive.length - i - 1];
            massive[massive.length - i - 1] = tmp;
        }
    }
}