Java 中把一个字符串反转

方法一：

    private static String reverse01(String str) {
        if (str == null || str.length() == 0) {
            return null;
        }
        StringBuilder sb = new StringBuilder(str.length());
        for (int i = str.length() - 1; i >= 0; i--) {
            sb.append(str.charAt(i));
        }
        return sb.toString();
    }