如何操作数组.求平均值.初级Java [英] How to manipulate arrays. Find the average. Beginner Java

问题描述

我有一个家庭作业，我想知道是否有人可以帮助我，因为我是 Java 和编程的新手并且被困在一个问题上.问题是:

I have a homework assignment and I was wondering if anyone could help me as I am new to Java and programming and am stuck on a question. The question is:

第一种方法求整数数组元素的平均值:

The first method finds the average of the elements of an integer array:

public double average(int[] data)

即给定一个整数数组，数据，计算其元素的平均值，均返回平均值.例如，{1, 3, 2, 5, 8} 的平均值为 3.8.

That is, given an integer array, data, calculate the average of its elements are return the average value. For example, the average of {1, 3, 2, 5, 8} is 3.8.

这是我到目前为止所做的:

Here is what I have done so far:

public double average(int[] data) {  
    int sum = 0;

    while(int i=0; i < data.length; i++) 

    sum = sum + data[i]; 
    double average = sum / data.length;; 

    System.out.println("Average value of array element is " " + average);
}

在编译它时，我在 int i=0 部分收到一条错误消息，说.class expected".任何帮助，将不胜感激.

When compiling it I get an error message at the int i=0 part saying '.class expected'. Any help would be appreciated.

推荐答案

使用增强的 for 会更好:

Using an enhanced for would be even nicer:

int sum = 0;
for (int d : data) sum += d;

另一件可能会让你大吃一惊的事情是你将获得的错误结果

Another thing that will probably give you a big surprise is the wrong result that you will obtain from

double average = sum / data.length;

原因:右侧有整数除法，Java 不会自动将其提升为浮点除法.它将计算 sum/data.length 的整数商，然后才将该整数提升为 double.一个解决方案是

Reason: on the right-hand side you have integer division and Java will not automatically promote it to floating-point division. It will calculate the integer quotient of sum/data.length and only then promote that integer to a double. A solution would be

double average = 1.0d * sum / data.length;

这将强制被除数变成 double，它会自动传播到除数.

This will force the dividend into a double, which will automatically propagate to the divisor.

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