Question

String num = in.next(); if (num.matches("\\d+")) 这是什么意思

import java.util.Scanner;

public class Huiwen {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
String num = in.next();
if (num.matches("\\d+")) {
StringBuffer sb = new StringBuffer(num);
StringBuffer sb1 = sb.reverse();
System.out.println(sb1);
if(sb1.equals(sb)){
System.out.println("回文");
}
}
}
}
刚接触java，什么都不懂，各位帮帮忙啊，如果可能的话，最好都帮我注释一下，谢谢了

Answer 1

Scanner in = new Scanner(System.in); 等待输入
String num = in.next();获取输入数据
if (num.matches("\\d+")) { 判断数据是否是数字