Codewars 6 kyu Kata: Detect Pangram

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A pangram is a sentence that contains every single letter of the alphabet at least once. For example, the sentence "The quick brown fox jumps over the lazy dog" is a pangram, because it uses the letters A-Z at least once (case is irrelevant).

Given a string, detect whether or not it is a pangram. Return True if it is, False if not. Ignore numbers and punctuation.

import java.util.*;

public class PangramChecker
{    

    public boolean check( String sentence )
    {
        HashSet< Character > ans =
            new HashSet<>();
        HashSet< Character > chars =
            new HashSet<>();
        sentence = sentence.toUpperCase();
        
        for ( char ch = 'A'; ch <= 'Z'; ch++ )
        {
            chars.add( ch );
        }
        
        for ( Character ch : sentence.toCharArray() )
        {
            if ( chars.contains( ch ) )
            {
                ans.add( ch );
            }
        }
        
        return ans.size() == 26;
    }
    
}