方法不兼容的类型

Question

import java.util.*;
import java.lang.Math;

class StandardDeviation{
  public static void main(String args[]){
    ArrayList<Double> numbers = new ArrayList<Double>();
    Scanner kb=new Scanner(System.in);
    double in=kb.nextDouble();
    while(in!=-1){
        numbers.add(kb.nextDouble()); 
    }
    double avg = getAvg(numbers);
    double stdD = getD(avg,numbers);// tells me these are incompatible types
    System.out.printf("%f\n",stdD);
  }

  public static double getAvg(ArrayList<Double> numbers){
    double sum = 0.0;
    for (Double num : numbers){
        sum+= num;
    }
    return sum/numbers.size();
  }

  public static void getD(double avg, ArrayList<Double> numbers){
    ArrayList<Double> newSet = new ArrayList<Double>();
    for (int i = 0; i < numbers.size(); i++){
        newSet.add(Math.pow(numbers.get(i)-avg,2));
    }
    double total = 0.0;
    for (Double num : newSet){
        total += num;
    }
    double mean =(total/numbers.size());
    return Math.sqrt(mean);
  }
}

我太累了，我已经很累了，我什至不确定它是否能打印出正确的答案，但现在它告诉我double stdD = getD（avg，numbers）; 有不兼容的类型，不确定什么不兼容预先感谢

Answer 1

getD是无效的，它不返回值。 目前是

public static void getD(double avg, ArrayList<Double> numbers){

但这应该是

public static double getD(double avg, ArrayList<Double> numbers){

Answer 2

Your method is not returning anything. method return type is void and you are assigning that into double. that's why you are getting an error. Your method declaration should be like this - 

public static double getD(double avg, ArrayList<Double> numbers)