/**
     * 最后给个例子说明契约式编程的的简洁
     */

    /**
     * 防御式编程
     */
    public Integer get(Integer percent, List<Integer> counts){
        if(percent == null || counts == null){
            return null;
        }

        if(counts.size() == 0){
            return null;
        }

        if(percent < 0){
            throw new RuntimeException();
        }

        int sum=0;
        for (Integer count : counts) {
            if(count != null){
                sum += count;
            }
        }
        return sum;
    }

    /**
     * 契约式编程
     * 
     * @param percent percent 必须大于0，否则抛出异常
     * @param counts @NotEmpty注解提示调用方先判断size() > 0
     *               NoneNulList保证了容器中的元素不可能为null，将这判空这个过程前移到数据产生时
     * @return
     */
    public Integer get2(Integer percent, @NotEmpty NoneNulList<Integer> counts){

        // 业务相关的校验还是由本函数完成
        if(percent < 0){
            throw new RuntimeException();
        }

        int sum=0;
        for (Integer count : counts) {
            sum += count;
        }
        return sum;
    }