阅文19校招java后台编程题

一道是考的hashmap存储、查询、扩容、缩容原理及有哪些线程安全的map实现

还有一道是考输入1234 反转-4321 当时写的时候有思路 但是没有idea编译器一直在小方面出错 修改后代码如下：

public class ReverseNumber {

    public static void main(String[] args) {
        java.util.Scanner scanner = new java.util.Scanner(System.in);
        int num = scanner.nextInt();
        scanner.close();
        int result = reverse(num);
        System.out.println(result);
    }

    public static int reverse(int num) {
        String s = String.valueOf(num);
        String[] array;
        StringBuffer sb = new StringBuffer();
        char zf = s.charAt(0);
        if (zf != '-') {
            zf = '-';
            sb.append(zf);
            for (int i = s.length() - 1; i >= 0; i--) {
                sb.append(s.charAt(i));
            }
        } else{
            for (int i = s.length() - 1; i > 0; i--) {
                sb.append(s.charAt(i));
            }
        }

        String st = sb.toString();
        int last = Integer.valueOf(st);
        return last;
    }
}