Question

所以我正在为这次降雨分配写一个班级，我想我可以让它工作但是我遇到了程序最后一部分的问题“Rainfall rain = new Rainfall（）;”。

我知道到目前为止我的代码中可能存在一些逻辑错误，但我正专注于尝试至少将其打印出来以便我可以解决这些问题。谢谢！

/**
Rainfall.java calculated the total annual and average
monthly rainfall from the array. This program also returns
the month with the most rainfall and the month with the least rainfall.
*/


public class Rainfall 
{

  //set integer month to 12
  private int month = 12;

  private double[] months;

/**
    Constructor
    @param scoreArray An array of test scores
*/
  public Rainfall(double[] rainfallArray)
  {
     months = rainfallArray;
  }
//Get total annual rainfall
  public double getTotal() 
  {
     double total = 0;

    //for loop to go through the entire array to calculate the total amount of rainfall
     for (int i = 0; i < month; i++) 
     {
        total = total + months[i];
     }

     return total;
  }

//Calculate average monthly rainfall
  public double getAverage()
  {
     double total = 0; //To hold the current total amount of rainfall
     double average; //To hold the average amount of rainfall

     for (int i = 0; i < month; i++) 
     {
        total = total + months[i];
     }

    //Calculate average rainfall 
     average = total / (months.length + 1);

     return average;
  }
//Get month with the most rain
  public double getMost()
  {
     double most; //To hold the most amount of rainfall

    //set the first month in the array
     most = months[0];

     int m=0;


     for (int i = 0; i < month; i++) 
     {
        if (months[i] < most) 
        {
           m=i;
        }
     }
     return most;
  }

//Get month with the least rain
  public double getLeast()
  {
     double least; //To hold the least amount of rainfall
     int m=0;

    //set the first month in the array
     least = months[0];


     for (int i = 0; i < month; i++) 
     {
        if (months[i] < least) 
        {
           m = i;
        }
     }

     return least;
  }

  public static void main(String[ ] args) 
  {

     Rainfall rain = new Rainfall();
     rain.setMonths(); 

    //Display results of the Total, Avg, and Most and Least calculations of rainfall
     System.out.println("The total rainfall for the year: " + rain.getTotal());
     System.out.println("The average rainfall for the year: " + rain.getAverage());
     System.out.println("The month with most rain: " + rain.getMost());
     System.out.println("The month with least rain: " + rain.getLeast());
  }


}

Answer 1

更改构造函数以使用varargs参数：

public Rainfall(double... rainfallArray) {
    months = rainfallArray; // a varargs comes in as an array, ie double[]
}

然后当你构造它时，你可以传递任意数量的doubles（包括无）。

即所有这些都没问题：

Rainfall r1 = new Rainfall();
Rainfall r2 = new Rainfall(4);
Rainfall r3 = new Rainfall(4, 5, 6, 15);

请注意，在没有传递参数的情况下，即new Rainfall()仍然传入一个数组，但它的长度为零。

如果您想声明传入了特定的月份数，请将其添加到构造函数中：

if (rainfallarray.length != 12)
    throw new IllegalArgumentException(
        "Expecting 12 months of data, but only got " + rainfallarray.length);

Answer 2

问题是你的构造函数期望一个名为double array的{{1}}并且构造函数不包含任何参数;它是空的。用双数组初始化它将构造。

像这样：

rainfallArray

此外，您的double [] rain = {1.3, 2.4, 3.5, 6.2}; Rainfall rain = new Rainfall(rain); ... rest of code in main应如下所示：

for loops

如果按照以前的方式执行，如果没有大小为12个元素的数组，则会出现空指针异常。另外，请记住，数组是基于0的，因此您希望以1开始for循环，或者如果您使用现在使用的逻辑，则将for (int i = 0; i < months.size(); i++) { if (months[i] < most) { m=i; } }变量设置为11。

Answer 3

你的Rainfall类需要数据，你已经在构造函数中决定了（它必须有一个双精度数组）并且当你尝试构造一个没有数据的Rainfall对象时你违反了自己的规则，因此就是错误。您必须传递一个双精度数组（即使它不包含数据），以使对象以有效状态存在（根据您的规则，构造函数定义）。

所以new Rainfall()无效。你必须传递一个双数组。

double[] data = new double[12];
//fill in data, do stuff
Rainfall rain = new Rainfall(data);

错误：构造函数无法应用于给定类型

3 个答案: