java笔试之字符串反转

写出一个程序，接受一个字符串，然后输出该字符串反转后的字符串。

package test;

import java.util.Scanner;

public class exam04 {
    public static void main(String[] arg) {
        Scanner scanner = new Scanner(System.in);

        while (scanner.hasNext()) {
            String str = scanner.next();
            System.out.println(reserveStr1(str));
            reserveStr2(str);
            reserveStr3(str);
        }

    }

    public static StringBuilder reserveStr1(String str) {
        // 方法1
        StringBuilder sb = new StringBuilder(str);
        sb.reverse();
        return sb;
    }

    public static void reserveStr2(String str) {
        // 方法2：输入的数放入char数组中，按逆序放置
        int len = str.length();
        char[] ch = new char[len];
        for (int i = 0; i < len; i++) {
            ch[len - i - 1] = str.charAt(i);
        }
        System.out.println(String.valueOf(ch));
    }

    public static void reserveStr3(String str) {
        // 方法3
        char[] chars = str.toCharArray();
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < chars.length; i++) {
            sb.append(chars[chars.length - i - 1]);
        }
        System.out.println(sb.toString());
    }
}