ArrayList 通过删除 Smallest 来计算平均值答案

【问题标题】：ArrayList Calculate Average by dropping SmallestArrayList 通过删除 Smallest 来计算平均值
【发布时间】：2016-07-18 02:57:01
【问题描述】：

我的代码有两个问题。 1）当我向我的数组列表添加值时，它没有给我正确的平均值，所以我知道我的 for 循环中的条件是关闭的，并且 2）它没有显示我的数组列表中的所有数字。它特别不显示第 0 个整数。

这是我的代码：

public class CalcAvgDropSmallest {  

    public static void main(String[] args) {       
       int lowNum = 0;  // # of the lowest numbers to be dropped
       double average;  // calcuates the mean of the sum and the lowest numbers dropped
       ArrayList<Double> inputs= getALInfo();
       lowNum = getLowestnum();
       average = calculateAvg(inputs, lowNum);
       getAvg(inputs, lowNum, average);

    }

    public static ArrayList<Double> getALInfo() {
        ArrayList<Double> inputs = new ArrayList<Double>(); 

        // Read Inputs
          Scanner in = new Scanner(System.in);
          System.out.println("Please enter 5 - 10 integers, Q to quit: ");         
          Double vals = in.nextDouble();

         while (in.hasNextDouble())
            {
               inputs.add(in.nextDouble());
            }             

        return inputs;     
    }   

    public static int getLowestnum() {        
        int lowNum = 0;

        // Reads Input value for # of lowest values dropped

        System.out.println("How many of the lowest values should be dropped?");
        Scanner in = new Scanner(System.in);
        lowNum = in.nextInt();

        return lowNum;

    }

    public static double calculateAvg(ArrayList<Double> inputs, int lowNum) {
        double sum = 0;
        double average = 0;                
        int i = 0;
        // Calcuates the average of the array list with the lowest numbers dropped

        for (i = 0; i < inputs.size(); i++) 
        {
            if (inputs.get(i) > lowNum) {
                sum = sum + inputs.get(i);
            }
        }
        average = (sum / inputs.size());        

       return average;
    }

    public static void getAvg(ArrayList<Double> inputs,int n, double average) {
       // It's adding all the values and dividing by the size of it, which is a problem
       // Also, it's not showing the 0th integer aand just straight to the 1st integer
      System.out.println("The average of the numbers " + inputs + " except the lowest " +n+ " is " +average);  
    }
}

【问题讨论】：

你正在扔掉第一个双输入！
这里：Double vals = in.nextDouble();。不要那样做，不要忽略第一个条目。你输入了 vals，但从来没有把它放到你的 ArrayList 中。

标签： java arraylist average

【解决方案1】：

首先，请编程到List 接口（而不是ArrayList 具体类型）。其次，您应该确保将您读取的每个值添加到您的List。然后，确保您读取了终止值（并丢弃它）；否则它将在缓冲区中挂起。最后，我会将Scanner 传递给方法（而不是在本地重新声明它）。喜欢，

public static List<Double> getALInfo(Scanner in) {
    List<Double> inputs = new ArrayList<>();
    System.out.println("Please enter 5 - 10 integers, Q to quit: ");
    while (in.hasNextDouble()) {
        inputs.add(in.nextDouble());
    }
    in.next();
    return inputs;
}

您可以简化 getLowestnum 之类的

public static int getLowestnum(Scanner in) {
    System.out.println("How many of the lowest values should be dropped?");
    return in.nextInt();
}

然后你的calculateAvg 应该对List 进行排序并取一个subList（丢弃lowNum 值），最后返回平均值。比如，

public static double calculateAvg(List<Double> inputs, int lowNum) {
    Collections.sort(inputs);
    return inputs.subList(lowNum, inputs.size()).stream()
            .mapToDouble(Double::doubleValue).average().getAsDouble();
}

然后main完成示例

public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    List<Double> inputs = getALInfo(in);
    int lowNum = getLowestnum(in);
    double average = calculateAvg(inputs, lowNum);
    System.out.printf("%.2f%n", average);
}

【讨论】：