平均计算，或者在一个ArrayList作为参数传递给函数 [英] Calculate average or take in an ArrayList as a parameter to a function

问题描述

是否有一个内置的方法来计算的整数ArrayList的平均

Is there a built-in method to calculate the average of an integer ArrayList?

如果没有，我可以做一个功能，将做到这一点，采取ArrayList中的名称，并返回其平均值？

If not, can I make a function that will do that by taking in the name of the ArrayList and returning its average value?

推荐答案

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;
}

有关更好的性能，使用 INT [] 而不是的ArrayList＆LT;整数方式＆gt;

For even better performance, use int[] instead of ArrayList<Integer>.

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