непонятки)

public class Solution {
    public static void main(String[] args)  {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String file1 = null;
        String file2 = null;
        String file3 = null;
        try {
            file1 = reader.readLine();
            file2 = reader.readLine();
            file3 = reader.readLine();
        }catch (IOException e) {
            e.printStackTrace();
        } finally {
            reader.close();
        }

        FileInputStream fis2 = null;
        FileOutputStream fos1 = null;
        int amount = 0;
        try {
            fis2 = new FileInputStream(file2);
            fos1 = new FileOutputStream(file1);
            byte[] buf = new byte[fis2.available()];
            amount = fis2.read(buf);
            fos1.write(buf, 0, amount);
        }catch (IOException e) {
            e.printStackTrace();
        } finally {
            fis2.close();
            fos1.close();
        }
        FileInputStream fis3 = null;
        FileOutputStream fo1 = null;
        try {
            fis3 = new FileInputStream(file3);
            fo1 = new FileOutputStream(file1, true);
            byte[] buf3 = new byte[fis3.available()];
            amount = fis3.read(buf3);
            fo1.write(buf3, 0, amount);
        }catch (IOException e) {
            e.printStackTrace();
        } finally {
            fis3.close();
            fo1.close();
        }
    }
}