如何获得数组中前两个数的平均值？

Question

我无法弄清楚如何获得阵列中前2个数字的平均值，然后是前3个数字。我在这些线路上出现错误。 average(numbers[0],numbers[1]));和average(numbers[0],numbers[1],numbers[2]));这里是我的代码。

public class NoVarargsTest{ 
    // calculate average 
    public static double average(double[] numbers){ 
     double total = 0.0; 
     // calculate total using the enhanced for statement 
     for (double d : numbers){     
      total += d; 
     }       
     return (total/(double)numbers.length); 
    } 
    public static void main (String[] args) { 
     double d1 = 10.0; 
     double d2 = 20.0; 
     double d3 = 30.0; 
     double d4 = 40.0; 

     double[] numbers= new double[4]; 
     numbers[0] = 10.0; 
     numbers[1] = 20.0; 
     numbers[2] = 30.0; 
     numbers[3] = 40.0; 

     if (args.length == 0) 
      System.out.println("No Command Line arguments"); 
     else { 

      System.out.println("You provided " + args.length 
        + " arguments"); 

      for (int i = 0; i < args.length; i++) { 
       System.out.println("args[" + i + "]: " 
         + args[i]); 
      } 
     } 

     System.out.printf("d1 = %.1f%nd2 = %.1f%nd3 = %.1f%nd4 = %.1f%n%n",numbers[0],numbers[1], numbers[2], numbers[3]); 
     System.out.printf("Average of d1 and d2 is %.1f%n", 
     average(numbers[0],numbers[1])); 
     System.out.printf("Average of d1, d2 and d3 is %.1f%n", 
     average(numbers[0],numbers[1],numbers[2])); 
     System.out.printf("Average of d1, d2, d3 and d4 is %.1f%n", 
     average(numbers)); 
    } 

} // end class NoVarargsTest 

Answer 1

如果你想使用可变参数，你必须声明你的方法签名：

public static double average(double... numbers){ 

numbers届时将你的方法中的double[]。

这由JLS §8.4.1: Formal Parameters指定。

Answer 2

你public static double average(double[] numbers)方法的参数是一个double []数组，但你只是通过两个双值这里：average(numbers[0],numbers[1]));

为了解决这个问题要么改变你的方法来public static double average(double... numbers)或传递一个数组：average(new double[] {numbers[0], numbers[1]})

Answer 3

import java.util.Arrays; 

public class NoVarargsTest 
{ 
    // calculate average 
    public static double average(double[] numbers) 
    { 

     double total = 0.0; 
     // calculate total using the enhanced for statement 
     for (double d : numbers) 
     { 
      total += d; 
     } 
     return total/(double)numbers.length; 
    } 

    // prints the wording around the array 
    private static void driver(double[] numbers) 
    { 
     System.out.println("The average of " + Arrays.toString(numbers) + " is "+average(numbers)); 
    } 

    public static void main(String[] args) 
    { 
     driver(new double[] {10}); 
     driver(new double[] {10, 20}); 
     driver(new double[] {10, 20, 30}); 
    } 

} // end class VarargsTest