Check if string is complete

public class CheckAllAlphabetsAlgorithms
{
    public static void main(String[] args)
    {
        System.out.println( checkAllChars( "qwertyuioplkjhgfdsAzxcvbnm" ) );
        System.out.println( checkAllChars( "123" ) );
        System.out.println( checkAllChars( "ejuxggfsts" ) );
        System.out.println( checkAllChars( "wyyga" ) );
    }
      
    private static String checkAllChars ( String input )
    {
        //If input length is less than 26 then it can never be complete
        if(input.length() < 26)
        {
            return "FALSE";
        }
                  
        for (char ch = 'A'; ch <= 'Z'; ch++)
        {
            if (input.indexOf(ch) < 0 && input.indexOf((char) (ch + 32)) < 0)
            {
                return "FALSE";
            }
        }
        return "TRUE";
    }
}