用可以使用整型数组来保存字符x出现的次数

public class Test {

public static void main(String[] args) {
        String s="google";
        
        Test t=new Test();
    System.out.println(t.FirstNotRepeatingChar(s)+1);
}
public int FirstNotRepeatingChar(String str) {
    int[] cnts = new int[256];
    for (int i = 0; i < str.length(); i++)
        cnts[str.charAt(i)]++;
    for (int i = 0; i < str.length(); i++)
        if (cnts[str.charAt(i)] == 1)
            return i;
    return -1;
}

}