java题目 任意一个字符串 倒置输出，保持单词的完整性

public static void main(String[] args) {
        StringBuffer sb = new StringBuffer("this is a apple");
        System.out.println(reverse(sb));
    }
    
    public static StringBuffer reverse(StringBuffer sb) {
        StringBuffer ret = new StringBuffer();
        char[] charArray = sb.toString().toCharArray();
        StringBuffer temp = new StringBuffer();
        for(int i = charArray.length-1; i >= 0; i--) {
            if ((charArray[i] >= 'a' && charArray[i] <= 'z') || 
                    (charArray[i] >= 'A' && charArray[i] <= 'Z')) {
                temp.append(charArray[i]);
                if (i==0) {
                    ret.append(temp);
                }
            } else {
                ret.append(temp);
                ret.append(" ");
                temp.delete(0, temp.length());
            }
        }
        return ret;
    }