如果我尝试在不同的公共类中将数组作为参数传递，为啥我的构造函数无法在 Java 中编译？

Posted 2023-02-25

【中文标题】如果我尝试在不同的公共类中将数组作为参数传递，为啥我的构造函数无法在 Java 中编译？

【英文标题】：How come my constructor will not compile in Java if I try and pass an array as an argument in a different public class?如果我尝试在不同的公共类中将数组作为参数传递，为什么我的构造函数无法在 Java 中编译？

【发布时间】：2013-12-08 02:01:16

【问题描述】：

我正在尝试编译此代码，但不断收到错误消息- 错误：/Users/Pedro/Dropbox/school/java/Proj/exam 3/EchoText.java:23：找不到符号 符号：构造函数 MultiPoint(java.lang.Double[]) 位置：多点类

如果我在公共 EchoText 的构造函数中省略该数组，它将编译。但是，我需要将数组作为参数传递给 MultiPoint 公共类。我的问题是为什么它不能与参数一起编译，这个错误到底是什么意思？

public class MultiPoint

    private double[] testCoord;

    public MultiPoint(double[] coordPt)
    
      testCoord = coordPt;
    

    public void printPoints()
    
        for ( int i = 0; i < coordPt.length; i++ )
        
            System.out.println("Coordinate # " + i + " : " + coordPt[ i ]);
        
        System.out.println("");
    


import java.util.Scanner;
import java.lang.Math;
import java.util.ArrayList;

public class EchoText

  private static String ans = null;

  public static double number, coord;
  private static int counter =0;
  private static ArrayList <Double> coordList = new ArrayList<Double>();
  public static void main(String[] args)
  

    mainDeal(); 
    Double coordPt[] = new Double[ coordList.size() ];
    coordList.toArray(coordPt);

    for (Double list1 : coordPt)
    
      System.out.println((counter + 1) + list1);
       
    MultiPoint myMultiPoint = new MultiPoint(coordPt);
  
   // HELP MENU CREATED BY PROF. BLANDO! I DO NOT TAKE CREDIT FOR THE HELP MENU TEXT!
   public static void helpMenu()
   
     System.out.println("****************************** LAB 7 HELP MENU ******************************");
     System.out.println("\t\t\tBy Pedro Estrada");
     System.out.println("* This program defines a point in a N-Dimensional space. ");
     System.out.println("    - Each point can have different number of non-zero coordinate");
     System.out.println("    - You may request a random number for any coordinate by typing \"RANDOM\"");
     System.out.println("    - When you are finished entering the coordinate just press the <Enter> key");
     System.out.println();
     System.out.println("* Pairs of point are used to create a lines");
     System.out.println("    - If the 2 points have mismatched dimensions, the point from the lower-dimension space is");
     System.out.println("      converted to a higher dimension point with added coordinate of 0");
     System.out.println("    - When a line is created, the line distance is provided");
     System.out.println();
     System.out.println("* When you are done specifying points and lines type \"EXIT\" to display final operation statistics");
     System.out.println("* All key words are case insensitive and can be abbreviated");
     System.out.println("* Random number will be scaled between -1,000.00 and +1,000.00");
     System.out.println();
     System.out.println("****************************** LAB 7 HELP MENU ******************************");
   
   public static String userPrompt()
   
     Scanner keyboard = new Scanner(System.in);
     System.out.println("Enter a coordinate: [R]andom: [H]elp: [E]xit to exit program: Enter key  for next point:");
     return keyboard.nextLine();
   
   public static void mainDeal()
   

     /** I pulled some code from this website:
      * http://www.java-forums.org/new-java/19024-detect-enter-key-being-pressed.html
      */
      while(true)
      
      ans = userPrompt();

      if((ans == null)|| (ans.length() == 0) ||(ans.trim().equals("")))
      
         System.out.println("Exiting...");
         break;
      
      else if (ans.trim().toUpperCase().charAt(0) == 'R')
      
        coord = Math.random();
        counter++;
        coordList.add(coord);

      
      else if (ans.trim().toUpperCase().charAt(0) == 'E')
      
        System.exit(0);
      
      else if (ans.trim().toUpperCase().charAt(0) == 'H')
      
        helpMenu();
      
      else
      
        coord = Double.parseDouble(ans);
        counter++;
        coordList.add(coord);
      
    
   

【参考方案1】：

MultiPoint 构造函数接受double[] 类型，如下所示：

public MultiPoint(double[] coordPt)

但是，当您创建 MultiPoint 的新实例时，您将传递一个 Double[] 类型，如下所示：

Double coordPt[] = new Double[ coordList.size() ];
MultiPoint myMultiPoint = new MultiPoint(coordPt);

【参考方案2】：

Java 会自动为您将Double 转换（拆箱）为double，但它不会为数组做同样的事情。你用Double[] 调用你的构造函数，它期待double[]。

【讨论】：

我将所有与数组相关的代码从 double[] 转换为 Double[] 并编译。谢谢。