編寫一個程式，實作字元串大小寫的轉換并倒序輸出

public class Test01 {
  public static void main(String[] args) {
    String str = "HelloWorld";
    // 字元串轉成char數組
    char[] ch = str.toCharArray();
    StringBuffer buffer = new StringBuffer();
    for (int i = str.length() - 1; i >= 0; i--) {
      if (ch[i] >= 'A' && ch[i] <= 'Z') {
        buffer.append(String.valueOf(ch[i]).toLowerCase());
      } else if (ch[i] >= 'a' && ch[i] <= 'z') {
        buffer.append(String.valueOf(ch[i]).toUpperCase());
      }
    }
    System.out.println(buffer.toString());
  }
}