Java - for循环终止表达式之间的区别 [英] Java - Difference between for loop terminating expression

问题描述

我只是好奇：这两个循环实现之间的速度和性能是否存在差异？假设 size（）方法返回处理一组元素的数组，集合或对象的长度（实际上它来自 XOM api）。

I'm just curious: Is there a difference on speed and performance between this two loops implementation? Assume that size() method returns the length of the array,collection, or object that handles a group of elements (actually it's from XOM api).

实施1：

int size = someArray.size();
for (int i = 0; i < size; i++) {
    // do stuff here
}

实施2：

for (int i = 0; i < someArray.size(); i++) {
    // do stuff here
}

推荐答案

从绩效的角度来看，差别不大。这是因为可以优化循环，以便内联size（）查找，导致性能差异很小。

From a performance point of view, there is little difference. This is because a loop can be optimized so that the size() lookup is inlined, resulting in very little performance difference.

主要区别在于循环时大小是否发生变化。第一种情况将尝试迭代固定次数。在第二种情况下，迭代次数将取决于最终大小（）。

The main difference is if the size changes while looping. The first case will try to iterate a fixed number of times. In the second case, the number of iterations will depend on the final size().

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