import java.util.*;
import java.lang.String；
class JudgeArr{
    boolean flag=true;
    boolean judArr(String s){
        for(int i=0;i<(s.length()/2);i++){
            char a=charAt(i);
            char b=chatAt(s.length()-i);
            if (a!=b) flag=false;
            }
        return flag;   
    }
}
public class Judge {
    public static void main(String args[]){
        Scanner scan=new Scanner(System.in);
        JudgeArr judgearr=new JudgeArr();
        System.out.println("Please input");
        String s=scan.next();
        boolean flag=judgearr.judArr(s);
        System.out.println(flag);
    }
}

为什么我用你这个在Eclipse运行会出现The method charAt(int) is undefined for the type JudgeArr

就是直接用了你的