Count the unique character in a String

public static int frq [] = new int [500];    
public static int countUniqueChar (String line) {
      Arrays.fill(frq, 0);
      int ans = 0;
      for(int i = 0; i < line.length(); ++i) {
          if(frq[line.charAt(i)] == 0) {
              frq[line.charAt(i)]++;
              ++ans;
          }
      }
      return ans;
}  

input
“aaaaaa”
“aaa aaa”
“abcdeabcde”
“YESyes”

output
1
2
5
6

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