Question

我想调用此方法从数组中获取中值。该方法声明为public double getMedian(double[]list){//code}。

我尝试将方法调用为getMedian(double,list)，但我收到了错误消息。调用该方法的正确方法是什么？

这是完整的方法：

public double getMedian(double[] list) {
    // calculate the length of the entries
    // create an iterator
    int factor = list.length - 1;
    double[] first = new double[(int) ((double) factor / 2)];
    double[] last = new double[first.length];
    double[] middleNumbers = new double[1];

    for (int i = 0; i < first.length; i++) {
        first[i] = list[i];
    }

    for (int i = list.length; i > last.length; i--) {
        last[i] = list[i];
    }

    for (int i = 0; i <= list.length; i++) {
        if (list[i] != first[i] || list[i] != last[i])
            middleNumbers[i] = list[i];
    }

    if (list.length % 2 == 0) {
        double total = middleNumbers[0] + middleNumbers[1];
        return total / 2;
    } else {
        System.out.println(middleNumbers);
        return middleNumbers[0];
    }
}

Answer 1

该方法将double值数组作为参数。您可能希望创建一个double数组并传递：

double[] values = {0.1d, 0.3d, 0.5d, 1.0d, 1200.0d};        
double median = this.getMedian(values); // should return 0.5d

但是getMedian方法有一些逻辑错误阻止它正常工作。特别是，第二个循环开始超出数组的范围：

 for (int i = list.length; i > last.length; i--) {
     last[i] = list[i];
 }

使用我的测试数据，i从5开始，倒计时直到i大于5，但该数组只包含从{{1}开始索引的元素} 0。

Answer 2

它只需要一个double，list就是你刚刚创建的数组名称。你需要做

getMedian(double[] doubleArray, List list)

在调用它时使用2种不同的类型。

Answer 3

像这样（包括可以说是更优雅，更有效的getMedian版本）：

public class Test 
{
    public double getMedian(double[] list)
    {
        double median = 0;

        if (list != null && (list.length > 0)) 
        {
            // Sort ascending
            Arrays.sort(list);

            int numItems = list.length;

            if ((numItems % 2) == 0)
            {
                // We have an even number of items - average the middle two
                int middleIndex = numItems / 2;
                double firstMiddleValue = list[middleIndex - 1];
                double secondMiddleValue = list[middleIndex];
                median = (firstMiddleValue + secondMiddleValue) / 2;
            } 
            else
            {
                // Odd number of items - pick the middle one
                median = list[(numItems / 2)];
            }
        }

        return median;
    }

    public static void main(String[] args)
    {
        Test t = new Test();

        double[] testValuesOfLengthOne = { 3.1415 };
        double[] testValuesEvenLength = {22.5, 14.33, 100.849, 44.259, 0.0, 145000.0};
        double[] testValuesOddLength = {22.5, 14.33, 100.849, 44.259, 0.0,  145000.0, -4.9};

        System.out.println("Median of " + Arrays.toString(testValuesOfLengthOne)    + " is " + t.getMedian(testValuesOfLengthOne));
        System.out.println("Median of " + Arrays.toString(testValuesEvenLength) + " is " + t.getMedian(testValuesEvenLength));
        System.out.println("Median of " + Arrays.toString(testValuesOddLength) + " is " + t.getMedian(testValuesOddLength));
    }
}

这为您提供以下输出：

Median of [3.1415] is 3.1415
Median of [22.5, 14.33, 100.849, 44.259, 0.0, 145000.0] is 33.3795
Median of [22.5, 14.33, 100.849, 44.259, 0.0, 145000.0, -4.9] is 22.5

如何使用签名调用方法＆＃34; public double getMedian（double [] list）{// code}＆＃34;

3 个答案: