Write a Java program to find the index of first non-repeating character in a given string

import java.util.*;
public class Solution {
 public static void main(String[] args) {
  String str1 = "google";
  System.out.println("Index of first non-repeating character in '" + str1 + "' is: " + first_unique_character(str1));
 }

 public static int first_unique_character(String str1) {
  HashMap < Character, Integer > map = new HashMap < > ();
  for (int i = 0; i < str1.length(); ++i) {
   char chr = str1.charAt(i);
   map.put(chr, map.containsKey(chr) ? map.get(chr) + 1 : 1);
  }
  for (int i = 0; i < str1.length(); ++i) {
   if (map.get(str1.charAt(i)) < 2) {
    return i;
   }
  }
  return -1;
 }
}

Sample Output:

Index of first non-repeating character in 'google' is: 4