找出第一次出现重复的字符

找出第一次出现重复的字符

import java.util.HashMap;

public class Solution{
    public static Character findRepeatString(String str){
        Character repeatString = null;
        Map<Character,Integer> map = new HashMap<Character,Integer>();
        for(int i=0;i<str.length();i++){
            if(map.containsKey(str.charAt(i))){
                repeatString= str.charAt(i);
                break;
            }else{
                map.put(str.charAt(i),1);
            }
        }
        return repeatString;
    }

    public static void main(String[] args){
        String str ="4det5gtrr'";
        System.out.println(findRepeatString(str));
    }
}