Question

我必须创建要使用其他人拥有的主类来实现的类，并且出于某种原因我没有得到正确的输出，我不确定这个错误来自何处。

预期产出：

中位数= 44.5

平均值= 49.300

SD = 30.581

public class StatPackage { 
int count; 
double [] scores; 



StatPackage() { 
count = 0; 
scores = new double[500]; 
} 
public void insert (double value) { 
if (count < 500){ 
scores[count] = value; 
++ count; 
} 
} 
public double Mean () { 
    double sum = 0; 
    //For loop for calculating average or mean
    for(int i = 0; i < count; i++){
            sum += (scores[i]);

    }
    double average = sum/count;  
    return average;
    } 

public double Median() { 
int min; 
int tmp; 
int size; 

for (int i = 0; i < count; i ++) 
{ 
min = i; 
for (int pos = i + 1; pos < count; pos ++) 
if (scores [pos] < scores [min]) 
min = pos; 

tmp = (int)scores [min]; 
scores [min] = scores [i]; 
scores [i] = tmp; 

} 
double median = 0;
if  (count % 2 == 0){
    median = (scores[scores.length/2-1] + scores[scores.length/2])/2;
}
else {
    median = (scores[((scores.length/2))]);
}
return median;
} 

public double Variance () { 
    double variance = 0;
    double sum = 0;
    //For loop for getting the variance
    for(int i = 0; i < count; i++){
        sum += scores[i];
        variance += scores[i] * scores[i];

    }
    double varianceFinal = ((variance/count)-(sum*sum)/(count*count));
    return (varianceFinal);
} 

public double StdDev (double variance) { 
    double sum = 0;
    for(int i = 0; i < count; i++){
        sum += scores[i];
        variance += scores[i] * scores[i];

    }
    double varianceFinal = ((variance/count)-(sum*sum)/(count*count));
return Math.sqrt(varianceFinal);

}

Answer 1

您的Median()方法存在问题。尝试更改

if  (count % 2 == 0){
    median = (scores[scores.length/2-1] + scores[scores.length/2])/2;
}
else {
    median = scores[scores.length/2];
}

到

if (count % 2 == 0)
    median = (scores[count/2] + scores[count/2 - 1])/2;
else
    median = scores[count/2];

因为您有一个包含500个元素的固定大小的数组，所以您拥有的代码将返回位置249和250处的项目的平均值，如果您的数组中的值少于251，则该值将为0。

Answer 2

在慈善/精神错乱中，我很快写了一个驱动程序，试图测试这个东西。

    public static void main(String[] args)
{
    StatsPackage sp = new StatsPackage();
    for (int i = 0; i < 101; ++i) {
        sp.insert(i);
    }

    System.out.println("count: " + sp.count);
    System.out.println("mean: " + sp.Mean());
    System.out.println("median: " + sp.Median());
    System.out.println("variance: " + sp.Variance());
}

除了中位数没有计算正确的值（并且@BadCash可能有解决该问题的方法）之外，没有抛出ArrayOutOfBounds。

编辑：将更新作为@BadCash推荐给Median方法似乎解决了中位数没有给出正确答案。

ArrayOutOfBoundsException错误？

2 个答案: