计算2进制数中1的个数

    /**     *      * @param number     * @return 返回number中1的个数      */    public static int count(int number) throws IllegalArgumentException {        if(number < Integer.MIN_VALUE || number > Integer.MAX_VALUE)            throw new IllegalArgumentException("number is illegal");        if (number < 0) {            number = -number;        }        int n = 0;        while (number > 0) {            n += number & 1;            number >>>= 1;                  }        return n;    }