字符串反转

1.递归实现字符串反转

     public static String reverseStr(String str) {
        int length = str.length();
        if (length <= 1) {
            return str;
        }
        return reverseStr(str.substring(1)) + str.charAt(0);
    }

2.charAt()

  /**
     * 该方法是通过charAt()方法获得每一个char的字符，
     * i=0时获得第一个字符a然后赋值给reverse
     * 此时reverse="a";i=1时获得第二个字符b
     * 然后加上reverse再赋值给reverse，此时reverse="ba";
     * 依次类推
     */
    public static String reverseCharAt(String s) {
        int length = s.length();
        String reverse = "";
        for (int i = 0; i < length; i++)
            reverse = s.charAt(i) + reverse;
        return reverse;
    }

3.charArray

    public static String reverseCharArray(String s) {
        char[] array = s.toCharArray();
        String reverse = "";
        for (int i = array.length - 1; i >= 0; i--) {
            reverse += array[i];
        }
        return reverse;
    }

4.StringBuilder

    /**
     * StringBuilder 的reverse()
     *
     * @param s
     * @return
     */
    public static String reverseStringBuilder(String s) {
        StringBuilder sb = new StringBuilder(s);
        String reverseStr = sb.reverse().toString();
        return reverseStr;
    }