整数反转

方法一

转化成Char[]来解

import java.util.Scanner;

public class Reverse {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            String n = sc.next();
            boolean flag = false;
            char[] arr = n.toCharArray();
            char[] newArr;
            if (arr[0] == '-') {
                flag = true;
                newArr = new char[arr.length - 1];
                for (int i = 1; i < arr.length; i++) {
                    newArr[newArr.length - i] = arr[i];
                }
            } else {
                newArr = new char[arr.length];
                for (int i = 0; i < arr.length; i++) {
                    newArr[arr.length - 1 - i] = arr[i];
                }
            }
            String res = String.valueOf(newArr);
            if (flag) {
                System.out.println(Integer.parseInt(res) * -1);
            } else {
                System.out.println(Integer.parseInt(res));
            }
        }
    }
}

方法二

转换成String来解

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int flag = 1; if (n < 0 ) { flag = -1; n = -n; }
        StringBuilder sb = new StringBuilder(String.valueOf(n));
        System.out.println(Integer.valueOf(sb.reverse().toString()) * flag);
        return;
    }
}

方法三

数学方法

public class Main {
    public static int reverse(int x) {
        int rev = 0;
        while (x != 0) {
            rev = rev * 10 + x % 10;
            x /= 10;
        }
        return rev;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int input = in.nextInt();
        System.out.println(reverse(input));
    }
}