找不到符号 - 变量，尽管声明了变量

Question

numThrows 变量引发了在主方法中使用时未找到变量的错误。即使我在其中一种方法中声明了它。我使用在 void 提示方法中声明变量。该程序旨在使用随机坐标计算 Pi，然后使用公式根据用户给定的尝试次数来估算饼图。

import java.util.Random;
import java.util.Scanner;
import java.io.PrintWriter;
import java.io.File;
import java.io.IOException;
public class Darts




 public static void prompt()
 {
     Scanner in = new Scanner(System.in);
    System.out.println("How many throws per trial would you like to do?: ");
    int numThrows = in.nextInt();
    System.out.println("How many trials would you like to do?: ");
    int numTrials = in.nextInt(); 



    }


 public static double[] randomX( int numThrows)
 {
     int darts = 0;
     int i = 0;
     double[] cordX = new double[numThrows];
     while(darts <= numThrows)
     {
         cordX[i] = Math.random();
         i++;
        }
     return cordX;
    }
 public static double[]randomY(int numThrows)
 {
     int darts = 0;
     int i = 0;
     double [] cordY = new double[numThrows];
     while(darts <= numThrows)
     {
         cordY[i] = Math.random();
         i++;
        }
     return cordY;


    }
 public static void getHits(int numThrows, double[] cordX, double[] cordY)
 {
     int ii = 0;
     int i = 0;
     double hits = 0;
     double misses = 0;
     for(i = 0; i <= numThrows; i++)
      {
     if( Math.pow(cordX[ii],2) + Math.pow(cordY[ii],2) <= 1)
     {
         hits++;
         ii++;

        }
        else{
            misses++;
        }
    }

    }
 public static double calcPi(int misses, int hits)
{
    int total = hits + misses;
    double pi = 4 * (hits / total);

}
// public static void print(double pi, int numThrows)
// {

   //  System.out.printf("  %-7s         %3.1f            %7s\n", "Trial[//numtrial]: pi = "

 //   }


   public static void main(String[] args)throws IOException
    {
     prompt();
     double[] cordX = randomX(numThrows);
     double[] cordY = randomY(numThrows);
     gethits();
     double pi = calcPi(misses, hits);

}

}

Answer 1

numThrows 是提示方法的实例变量。如果你想做我认为你想做的事，请将 numThrows 设置为任何方法之外的静态变量。

它看起来像这样：

public class Darts {
    public static int numThrows
    public static int numTrials

可以从任何方法引用这些变量。这应该可以解决它。

Answer 2

如果 numThrows 在另一个函数中声明，那么它的 scope 不会扩展到 main 方法。

相反，如果您想在 main 方法和另一个方法中都使用它，请将其设为 class 实例。

例如：

class SomeClass {
    public static int numThrows = 2;
    public static void test() {
        numThrows = 4; // it works!
    }
    public static void main(String[] args) {
        System.out.println(numThrows); // it works!
    }
}

因此，它的范围将扩展到 class 的所有成员，而不仅仅是方法。

Answer 3

尝试删除prompt()未使用的方法，并将其块放在main方法中。

 public static void main(String[] args)throws IOException
  {
   Scanner in = new Scanner(System.in);
    System.out.println("How many throws per trial would you like to do?: ");
    int numThrows = in.nextInt();
    System.out.println("How many trials would you like to do?: ");
    int numTrials = in.nextInt(); 
    double[] cordX = randomX(numThrows);
    ...

找不到符号 - 变量，尽管声明了变量

Cannot find Symbol - Variable, despite the variable being declared

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