I am trying to write a small program that takes a `String` sentence (given in `main method`), and calculates the number of upper case characters and number of a's. I am having a bit of trouble with the second part. 

While there are no doubt multiple ways to write the program, I have written `for loops` that trace through the `String`, and do my work. It works fine for calculating the uppercase values, but for the a's, it is counting every letter as one. I may be going crazy. 

```
public class CountCharacters {
    public static void main(String[] args) {

        charCount("How many UPPER CASE letters, a's, and 0-9 digits are there in this String?"); 
    }

    public static void charCount(String b) {
        int upper = 0;
        int a = 0;
        for (int i = 0; i < b.length(); i++) {
            char v = b.charAt(i);
            if (Character.isUpperCase(v)) {
                upper++;
            }

        }

        for (int i = 0; i < b.length(); i++) {
            char t = b.charAt(i);
            if (Character.isLetter('a')) {
                a++;
            }
        }
        System.out.println("There are " + upper + " upper case letters, and " + a + " lower case a's in the String");
    }
}

```