不借助内置函数实现字符串反转输入I am a student.输出
.tneduts a ma I

import java.util.Scanner;public class Main{public static void main(String[] args) {Scanner sc = new Scanner(System.in);String str = sc.nextLine();int length = str.length();String reverse = "";for (int i = 0; i < length; i++) {reverse = str.charAt(i) + reverse;}System.out.println(reverse);}
}

方法一：（利用递归实现）public static String reverse1(String s) {int length = s.length();if (length <= 1)return s;String left = s.substring(0, length / 2);String right = s.substring(length / 2, length);return reverse1(right) + reverse1(left);  //调用递归
     }方法二：（拼接字符串）public static String reverse2(String s) {int length = s.length();String reverse = "";for (int i = 0; i < length; i++)reverse = s.charAt(i) + reverse;return reverse;}方法三：（利用数组，倒序输出）public static String reverse3(String s) {char[] array = s.toCharArray();String reverse = "";for (int i = array.length - 1; i >= 0; i--)reverse += array[i];return reverse;}方法四：（利用StringBuffer的内置reverse方法）public static String reverse4(String s) {return new StringBuffer(s).reverse().toString();}方法五：（利用临时变量，交换两头数值）public static String reverse5(String orig) {char[] s = orig.toCharArray();int n = s.length - 1;int halfLength = n / 2;for (int i = 0; i <= halfLength; i++) {char temp = s[i];s[i] = s[n - i];s[n - i] = temp;}return new String(s);}方法六：（利用位异或操作，交换两头数据）public static String reverse6(String s) {char[] str = s.toCharArray();int begin = 0;int end = s.length() - 1;while (begin < end) {str[begin] = (char) (str[begin] ^ str[end]);str[end] = (char) (str[begin] ^ str[end]);str[begin] = (char) (str[end] ^ str[begin]);begin++;end--;}return new String(str);}方法七：（利用栈结构）public static String reverse7(String s) {char[] str = s.toCharArray();Stack<Character> stack = new Stack<Character>();for (int i = 0; i < str.length; i++)stack.push(str[i]);String reversed = "";for (int i = 0; i < str.length; i++)reversed += stack.pop();return reversed;}