Как узнать, сколько раз каждый символ строки 'повторяется сам?

Question

Я искал и нашел некоторые подобные вопросы, но просто не могу понять, как применить их к моей проблеме. Пожалуйста, несите меня, так как это мой первый пост на сайте.

Мне нужно выяснить, сколько раз символ строки повторяется. Например, если данный "launch at noon", метод должен напечатать:

"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", 
};