java - 如何将命令行参数转换为 double 组以计算总和？

Question

所以目前我得到一个“Sum = 0.0”和一个 Mean 等于“NaN”，在与许多再次警告“从 double 到 int 的可能有损转换”的消息作斗争之后。我认为代码最终采用了 double 值，但仍然没有按照我的意愿执行:从命令行获取值，将它们放入数组中，对这些求和，然后计算平均值。

知道错误在哪里吗？

public class StudentMarks{

protected double[] marks;
//create an array filled with double values

public StudentMarks(double[] marks){
    this.marks = new double[0]; //set the default array size    
    }

    public void setMarks(){
    this.marks = marks;
    }

    public void getArray(){
        //one can only  print arrays using loops.. 
        //took me a little to realise that erm. 

        for(int i=0; i<marks.length; i++)
        System.out.println(marks[i]);
    }

    public double calSum(){

    double totals = 0.0;

    for(double i: marks) {
        //double mLength = Double.parseDouble(marks[i]);
        totals+= i;     
    }
        return totals;
    }

    //A method to calculate the mean of all elements

    public double calMean(){
        double means = (calSum()/marks.length);
        return means;
    }

    //A main method to test

    public static void main(String[] args) {
        // Check to see if the user has actually sent a paramter to the method
        if (args.length != 7){
            System.out.println("Usage: java RandomArray <NUM>. Example: java RandomArray 5");
            System.exit(-1);
        }

        double[] prompt = new double[args.length];
        for (int i =0; i<args.length; i++){
            prompt[i] = Double.parseDouble(args[i]);
        }
        StudentMarks test = new StudentMarks(prompt);


        test.getArray();

        // Calculate the sum of all the values in the array and print it
        System.out.println("Sum: "+ test.calSum());

        // Calculate the mean of all the values in the array and print it
        System.out.println("Mean: "+ test.calMean());
    }

}

Answer 1

代替

this.marks = new double[0];

使用

this.marks = marks;

您当前正在将 marks 成员变量分配为零长度数组而不是参数，因此元素之和为零，并且 marks.length为零，所以 calSum()/marks.length 为 0.0/0.0，定义为 NaN。