帮忙编写一个java程序

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class test {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringBuffer str = new StringBuffer(br.readLine());
        br.close();
        int len = str.length();
        for (int i = 0; i < len; ++i) {
            char c = str.charAt(i);
            if (Character.isLetter(c)) {
                if (Character.isLowerCase(c)) {
                    str.setCharAt(i, Character.toUpperCase(c));
                } else {
                    str.setCharAt(i, Character.toLowerCase(c));
                }
            } else {
                str.deleteCharAt(i);
                len = str.length();
                --i;
            }
        }
        System.out.println(str.reverse());
    }
}

太简单了呀