算法训练 大小写转换

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner in = new Scanner(System.in);
        StringBuffer str = new StringBuffer(in.next());
        for ( int i = 0 ; i < str.length() ; i++){
            char[] tmp = new char[1];
            tmp[0] = str.charAt(i);
            if ( tmp[0] >= 'A' && tmp[0] <= 'Z'){ 
                tmp[0] += 32;
                str.replace(i, i+1, new String(tmp));
            }else if ( tmp[0] >= 'a' && tmp[0] <= 'z'){ 
                tmp[0] -= 32;
                str.replace(i, i+1, new String(tmp));
            }
        }
        System.out.print(str.toString());
        in.close();
    }

}