Вопрос по Потоках System.in && System.setIn()

PrintStream InputStream defaultIn = System.in;
...
System.setIn(defaultIn);

{
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();
        sb.append("Olga").append("\n");
        sb.append("Vika").append("\n");
        sb.append("Nastya").append("\n");

        String st = sb.toString();
        byte[] d =  st.getBytes();
        InputStream input = new ByteArrayInputStream(st.getBytes());
        InputStream defaultIn = System.in;
        System.setIn(input);
        readLine();

        System.setIn(defaultIn);
        readLine();
    }
    public static void readLine(){
        BufferedReader buff = new BufferedReader(new InputStreamReader(System.in));
        try{
            while (buff.ready()) {
                String buble = buff.readLine();
                System.out.println(buble);
            }
        } catch (IOException e){
            e.printStackTrace();
        }
    }
}

System.setIn(input);
readLine();

System.setIn(defaultIn);
BufferedReader buff = new BufferedReader(new InputStreamReader(System.in));
String s = buff.readLine();
System.out.println(s);

Olga
Vika
Nastya
aasdfasd // это ввод
aasdfasd // это вывод