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);
    }
}

char a=s.charAt(i);
 char b=s.charAt(s.length()-i);
这只是表面的错误

import java.util.*;

class JudgeArr {
    boolean flag = true;

    boolean judArr(String s) {
        for (int i = 0; i < (s.length() / 2); i++) {
            char a = s.charAt(i);
            char b = s.charAt(s.length() - 1 - 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);
    }
}

输出：
Please input
1234554321
true

新手，努力学习中

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

你用我贴出来的代码试试

就是直接用了你的

package test;
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=charAt(s.length()-i);
            if (a!=b) flag=false;
            }
        return flag;   
    }
    private char charAt(int i) {
        // TODO 自动生成的方法存根
        return 0;
    }
}
public class Judge {
    public static void main(String args[]){
        @SuppressWarnings("resource")
        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);
    }
}
试试这个！！