java - "Incompatible Types"尝试从方法返回数组列表时

Question

在这个类中，我想返回整个数组列表，而不是作为单个元素。但是，我在编译时收到错误“不兼容类型”。我在这里做错了什么？感谢您的帮助!!

import java.util.ArrayList;
public class CO2FromElectricity
{



/**
 * Constructor for objects of class CO2FromElectricity
 */
public CO2FromElectricity()
{

}

public static double calcAverageBill(ArrayList<Double> monthlyBill, int ind) 
{
  ArrayList<Double> avgBill = new ArrayList<Double>();
  int i = ind;
  avgBill.set(i, (monthlyBill.get(i) + avgBill.get(i))/2); 
  return avgBill.get(i);    
}

public double calcAveragePrice(ArrayList<Double> monthlyPrice, int ind)
{
    int i = ind; 
    ArrayList<Double> avgPrice = new ArrayList<Double>();
    avgPrice.set(i, (monthlyPrice.get(i) + avgPrice.get(i))/2);
    return avgPrice;
}

public double calcElectricityCO2(double avgBill, double avgPrice)
{
    double avBill = avgBill;
    double avPrice = avgPrice; //Price per kilowatt that is...
    double emissions = (avBill/avPrice)*1.37*12; 
    return emissions;

}
}

Answer 1

在 calcAveragePrice() 方法中，您返回一个 List，而该方法被定义为返回一个 double。

要么将方法签名更改为

public List<Double> calcAveragePrice(...)

或者返回一个double

return list.get(i); //similar to the getAverageBill() method