How do I find out how many times each character of a string 's' repeats itself

Question

I have searched and found some similar questions, but just can't seem to figure out how to apply them to my problem. Please bear with me, as this is my first post on the site.

I have to find out how many times a character of a string repeats itself. For example, if given "launch at noon", the method should print:

"l" appears once in "launch at noon".
"a" appears twice in "launch at noon".
"u" appears once in " launch at noon ".
"n" appears 3 times in "launch at noon".
"c" appears once in "launch at noon".
"h" appears once in "launch at noon".
" " appears twice in "launch at noon".
"t" appears once in "launch at noon".
"o" appears twice in "launch at noon".

Answer 1

public void test() {
    // The string to test.
    String s = "launch at noon";
    // Count them.
    Map<Character, Integer> characterCounts = countCharacters(s);
    // Print the results.
    for (Map.Entry<Character, Integer> e : characterCounts.entrySet()) {
        int count = e.getValue();
        // Work out the name for the number.
        String number = count < specials.length 
                // The special short ones.
                ? specials[count] 
                // Is it a general one?
                : count < numbersAsWords.length
                // Yes
                ? numbersAsWords[count] + " times"
                // Way too many.
                : "too many times";
        // Print it.
        System.out.println("\"" + e.getKey() + "\" appears " + number + " in \"" + s + "\".");
    }
}

private Map<Character, Integer> countCharacters(String s) {
    // Map from character in string to count of occurrences.
    Map<Character, Integer> counts = new HashMap<>();
    // Walk the string.
    for (int i = 0; i < s.length(); i++) {
        // Get character at that point.
        char ch = s.charAt(i);
        // What's in the map for that character.
        Integer count = counts.get(ch);
        if (count == null) {
            // Not seen this character before - start at zero.
            count = 0;
        }
        // Increment seen count.
        count += 1;
        // Put it back in the map.
        counts.put(ch, count);
    }
    return counts;
}

// The short ones.
private static final String[] specials = {"not at all", "once", "twice"};

// The rest.
private static final String[] numbersAsWords = {"zero",
        "one",
        "two",
        "three",
        "four",
        "five",
        "six",
        "seven",
        "eight",
        "nine",
        "ten",
        "eleven",
        "twelve",
        "thirteen",
        "fourteen",
        "fifteen",
        "sixteen",
        "seventeen",
        "eighteen",
        "nineteen",
        "twenty",
        "twenty-one",
        "twenty-two",
        "twenty-three",
        "twenty-four",
        "twenty-five",
        "twenty-six",
        "twenty-seven",
        "twenty-eight",
        "twenty-nine",
        "thirty",
        "thirty-one",
        "thirty-two",
        "thirty-three",
        "thirty-four",
        "thirty-five",
        "thirty-six",
        "thirty-seven",
        "thirty-eight",
        "thirty-nine",
        "forty",
        "forty-one",
        "forty-two",
        "forty-three",
        "forty-four",
        "forty-five",
        "forty-six",
        "forty-seven",
        "forty-eight",
        "forty-nine",
        "fifty",
        "fifty-one",
        "fifty-two",
        "fifty-three",
        "fifty-four",
        "fifty-five",
        "fifty-six",
        "fifty-seven",
        "fifty-eight",
        "fifty-nine",
        "sixty",
        "sixty-one",
        "sixty-two",
        "sixty-three",
        "sixty-four",
        "sixty-five",
        "sixty-six",
        "sixty-seven",
        "sixty-eight",
        "sixty-nine",
        "seventy",
        "seventy-one",
        "seventy-two",
        "seventy-three",
        "seventy-four",
        "seventy-five",
        "seventy-six",
        "seventy-seven",
        "seventy-eight",
        "seventy-nine",
        "eighty",
        "eighty-one",
        "eighty-two",
        "eighty-three",
        "eighty-four",
        "eighty-five",
        "eighty-six",
        "eighty-seven",
        "eighty-eight",
        "eighty-nine",
        "ninety",
        "ninety-one",
        "ninety-two",
        "ninety-three",
        "ninety-four",
        "ninety-five",
        "ninety-six",
        "ninety-seven",
        "ninety-eight",
        "ninety-nine",
        "one hundred",
};