由于最大数可能超过Integer.MAX_VALUE,返回值用String返回:
static String maxNum(int [] array) {
        for (int i = 0;i < array.length;i ++) {
            for (int j = i;j < array.length;j ++) {
                int tmp;
                int maxI =array[i];
                int maxJ =array[j];
                maxI = Integer.valueOf(String.valueOf(array[i]) + String.valueOf(array[j]));
                maxJ = Integer.valueOf(String.valueOf(array[j]) + String.valueOf(array[i]));
                if (maxI > maxJ) {
                    tmp = array[j];
                    array[j] = array[i];
                    array[i] = tmp;
                }
            }
        }
        StringBuilder stringBuilder = new StringBuilder();
        for (int i = array.length - 1;i >= 0;i --) {
            stringBuilder.append(array[i]);
        }
        return stringBuilder.toString();
    }