java - 如何将整数列表与java流相加?
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();
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