我想总结一个整数列表.它的工作原理如下，但语法感觉不对.代码可以优化吗?

I want to sum a list of Integers. It works as follows, but the syntax does not feel right. Could the code be optimized?

Map<String, Integer> integers;
integers.values().stream().mapToInt(i -> i).sum();

推荐答案

这会起作用，但是 i ->i 正在做一些自动拆箱，这就是它感觉"的原因.奇怪的.mapToInt 将流转换为 IntStream 原始 int 值元素".以下任一方法都可以工作，并使用您的原始语法更好地解释编译器在幕后所做的事情:

This will work, but the i -> i is doing some automatic unboxing which is why it "feels" strange. mapToInt converts the stream to an IntStream "of primitive int-valued elements". Either of the following will work and better explain what the compiler is doing under the hood with your original syntax:

integers.values().stream().mapToInt(i -> i.intValue()).sum();
integers.values().stream().mapToInt(Integer::intValue).sum();