java 编写一个程序实现字符串大小写的转换并倒序输出

package cn;
public class Test01 {
	public static void main(String[] args) {
		String str= "HelloWorld";
		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());
	}

}