是否有内置方法来计算整数 ArrayList 的平均值？
如果没有，我可以创建一个函数，通过获取 ArrayList 的名称并返回其平均值来实现此目的吗？
这真的很简单：
// Better use a `List`. It is more generic and it also receives an `ArrayList`.
public static double average(List<Integer> list) {
// 'average' is undefined if there are no elements in the list.
if (list == null || list.isEmpty())
return 0.0;
// Calculate the summation of the elements in the list
long sum = 0;
int n = list.size();
// Iterating manually is faster than using an enhanced for loop.
for (int i = 0; i < n; i++)
sum += list.get(i);
// We don't want to perform an integer division, so the cast is mandatory.
return ((double) sum) / n;
}
为了获得更好的性能，请使用int[]代替ArrayList<Integer>.
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