有两道java题弄不懂，求助！

Question

1，从键盘输入一个字符，要求输出它在Unicode字符集中的前两个字符和后两个字符

2.

Answer 1

    public static void main(String []args) {
        int x1 = 0;
        int y1 = 0;
        int x2 = 3;
        int y2 = 4;
        double t = Math.sqrt(x2 * x2 + y2 * y2);
        System.out.println("2点之间的距离=" + t);
        String arr[]  = toUnicode("s");
        System.out.println("前两位=" + arr[0] + "；后两位=" + arr[1]); 
    }

    public static String[] toUnicode(String s){
        String arr[] = new String[2];
        String as[] = new String[s.length()];
        String s1 = "";
        for (int i = 0; i < s.length(); i++){
            as[i] = Integer.toHexString(s.charAt(i) & 0xffff);
            s1 = s1 + "\\u" + as[i];
        }
        System.out.println("字符转Unicode=" + s1);
        if(s1.length() > 2){
            arr[0] = s1.substring(0,2);
            arr[1] = s1.substring(s1.length() - 2,s1.length());
        }
        return arr;
    }