字符串反转

描述：字符串反转，即把字符串"abcd"变为"dcba"

public static void main(String[] args) {
		String str = "abc";
		System.out.println(reverse6(str));
	}

	public static String reverse6(String str) {
		int len = str.length();
		if (len <= 1) {
			return str;
		}
		String left = str.substring(0, len / 2);
		String right = str.substring(len / 2, len);
		return reverse6(right) + reverse6(left);
	}