java：Scanner类

Question

import java.util.*;
import java.util.regex.*;

public class test{
    public static void main(String[] args){
        Scanner reader=new Scanner(System.in);
        System.out.println("请输入要匹配的文本：");
        String a1=reader.next();
        System.out.println("要匹配的文本为："+a1);

        System.out.println("请输入正则表达式：");
        String b1=reader.next();
        System.out.println("正则表达式为："+b1);
        
        Pattern x = Pattern.compile(a1);
        Matcher y = x.matcher(b1);
        y.find();
        System.out.println(y.group());
        /* System.out.println(y.replaceAll("xx"));*/

    }
}

当正则表示输入带、.、+等符号是无法匹配，是什么原因呢？

Answer 1

    Pattern x = Pattern.compile(a1);
    Matcher y = x.matcher(b1);

a1 b1 写反了