import java.util.HashMap;
import java.util.Map;

public class Main {

    public Character findFirstRepeatChar(String s) {
        Map<Character, Integer> map = new HashMap<Character, Integer>();
        Character c;
        for (int i = 0; i < s.length(); i++) {
            c = s.charAt(i);
            if (map.containsKey(c)) {
                return c;
            }
            map.put(c, 0);
        }//for
        return null;//這裡要返回null，不能返回c
    }//findFirstRepeatChar

    public static void main(String[] args) {
        Main main = new Main();
        System.out.println(main.findFirstRepeatChar("kabcd%12234"));//輸出2
    }
}