public class Haeufigkeiten {

    /**
     *
     * @param srcString
     * @return
     */
    public static int[] countOccurances(String srcString){
        /*
        alloc an array with 65536 places (one for each possible unicode
        character). Java initializes each place to 0.
         */
        int[] resultArray = new int[65536];

        // helper vars, only i is really needed, we use the others for readability
        int i = 0;
        int idx;
        char currentChar;

        // loop over each char in the source string
        for (; i < srcString.length(); i++){
            // get current char
            currentChar = srcString.charAt(i);

            // cast char to int, to get the ascii/unicode number
            idx = (int)currentChar;

            // increment counter at the specific place
            resultArray[idx] += 1;
        }

        return resultArray;
    }

    public static void listOccurences(int[] resultArray){
        int i = 0;

        for (; i < resultArray.length; i++){
            if (resultArray[i] != 0)
                System.out.printf("Character '%c' found %d times.\n", i, resultArray[i]);
        }
    }

    public static int characterOccuredHowManyTimes(int[] resultArray,
            char character){
        return resultArray[(int) character];
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        int[] results;
        results = countOccurances("teststring");
        listOccurences(results);
        System.out.printf("Character t occured %d times.\n",
                          characterOccuredHowManyTimes(results, 't'));
        System.out.printf("Character z occured %d times.\n",
                characterOccuredHowManyTimes(results, 'z'));
    }

}