Question

我是初学Java用户，在不同的类中使用两个公共数组时遇到错误。该程序应该通过数学积分来模拟3个星际体。注意：我是这个网站的新用户，但尚无法确定格式。

package gravitationalmodel;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.Timer;

public class GravitationalModel 
{
  private Object timer;
  private GravitationalObject G1;
  private GravitationalObject G2;
  private GravitationalObject G3;
  public static double[] xArray;
  public static double[] yArray;
  final public double gravConst = 0.000000000067; 
  final public int refreshRate = 25;


  public GravitationalModel()
  {
    Timer timer = new Timer(refreshRate, (ActionListener) this); // refreshes model every 25 milliseconds
  }

  public static void main(String[] args) 
  {
    GravitationalObject G1 = new GravitationalObject(500, 500, 10, 10, 10); // creates 3 interstellar objects taking x position,
    GravitationalObject G2 = new GravitationalObject(400, 400, 10, 10, 10); // y position, x veleocity component, y velocity component
    GravitationalObject G3 = new GravitationalObject(600, 600, 10, 10, 10); // mass of the object


    xArray = new double[1920]; // assigns all elements of array to 0
    for (int x = 0; x < 1920; ++x)
    {
        xArray[x] = 0;
        //System.out.println(xArray[x]);
    }


    yArray = new double[1200];
    for (int x = 0; x < 1200; ++x)
    {
        yArray[x] = 0;
        //System.out.println(yArray[x]);
    }
  }

  public void actionPerformed(ActionEvent e) // refreshes model
  {
    G1.refreshVectorField();
    G2.refreshVectorField();
    G3.refreshVectorField();
    G1.refreshObjects();
    G2.refreshObjects();
    G3.refreshObjects();

  }
}

package gravitationalmodel;

public class GravitationalObject 
{
  private double xPos;   //location and speed of gravitational object
  private double yPos;
  private double vX;
  private double vY;
  private double mass;


  public GravitationalObject(double x, double y, double xv, double yv, double m)
  {
    xPos = x;
    yPos = y;
    vX = xv;
    vY = yv;
    mass = m;
  }

  public void refreshVectorField() // calculates gravitational field
  {
    int k = 1;
    for (int x = 0; x < 1920; ++x)
    {
      if (xPos > x)
        k = 1;
      else
        k= -1;
      if (xPos - x == 0)
        ++x;
      xArray[x] += k * (gravConst * mass) / Math.sqrt(xPos - x, 2.0); // errors on this line
    }
    for (int y = 0; y < 1200; ++y)
    {
      if (yPos < y)
        k = 1;
      else
        k= -1;
      yArray[y] += (gravConst * mass) / Math.sqrt(Math.abs(yPos - y), 2); //errors on this line
    }
  }

  public void refreshObjects()
  {
    vX += refreshRate/1000 * xArray[xPos]; // errors on these lines
    vY += refreshRate/1000 * yArray[yPos];
    xPos += refreshRate/1000 * vX;
    xPos += refreshRate/1000 * vX;
  }
}

Answer 1

您试图从GravitationalModel.xArray访问GravitationalObject而未完全限定静态字段。要么完全限定字段，要么在GravitationalModel中创建一个方法来完成工作。

请注意，Java中的公共可变字段通常不受欢迎，因为它会破坏封装。最好让对象通过方法封装数据和行为，并将变量保密。

Answer 2

作为初学者，你不应该快点。很快你就能写出很酷的节目了。这个程序中有很多错误，甚至程序也没有任何逻辑。你应该先练习一些小程序来获得基础知识。就像你创建了以下根本不使用的对象一样。

GravitationalObject G1 = new GravitationalObject(500, 500, 10, 10, 10); // creates 3 interstellar objects taking x position,
GravitationalObject G2 = new GravitationalObject(400, 400, 10, 10, 10); // y position, x veleocity component, y velocity component
GravitationalObject G3 = new GravitationalObject(600, 600, 10, 10, 10); // mass of the object

现在出现了程序错误。

如果要访问其他类中的实例变量gravConst或refreshRate，则需要创建类的对象并访问它们。或者你可以创建它们静态并将它们导入到像这样的类

import static gravitationalmodel.GravitationalModel.xArray; import static gravitationalmodel.GravitationalModel.yArray; import static gravitationalmodel.GravitationalModel.gravConst; import static gravitationalmodel.GravitationalModel.refreshRate;

Math.sqrt(double)不会带2个参数，因此我认为您要使用xArray[x] += k * (gravConst * mass) / Math.pow(xPos - x, 2.0);

并将double转换为int作为数组索引只能是整数，如下所示

vX += refreshRate / 1000 * xArray[(int)xPos]; vY += refreshRate / 1000 * yArray[(int)yPos];

所以你的最终节目如下：

package gravitationalmodel;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.Timer;

public class GravitationalModel {
    private Object timer;
    private GravitationalObject G1;
    private GravitationalObject G2;
    private GravitationalObject G3;
    public static double[] xArray;
    public static double[] yArray;
    final static public double gravConst = 0.000000000067;
    final static public int refreshRate = 25;

    public GravitationalModel() {
        Timer timer = new Timer(refreshRate, (ActionListener) this); // refreshes
                                                                        // model
                                                                        // every
                                                                        // 25
                                                                        // milliseconds
    }

    public static void main(String[] args) {
        GravitationalObject G1 = new GravitationalObject(500, 500, 10, 10, 10); // creates
                                                                                // 3
                                                                                // interstellar
                                                                                // objects
                                                                                // taking
                                                                                // x
                                                                                // position,
        GravitationalObject G2 = new GravitationalObject(400, 400, 10, 10, 10); // y
                                                                                // position,
                                                                                // x
                                                                                // veleocity
                                                                                // component,
                                                                                // y
                                                                                // velocity
                                                                                // component
        GravitationalObject G3 = new GravitationalObject(600, 600, 10, 10, 10); // mass
                                                                                // of
                                                                                // the
                                                                                // object

        xArray = new double[1920]; // assigns all elements of array to 0
        for (int x = 0; x < 1920; ++x) {
            xArray[x] = 0;
            // System.out.println(xArray[x]);
        }

        yArray = new double[1200];
        for (int x = 0; x < 1200; ++x) {
            yArray[x] = 0;
            // System.out.println(yArray[x]);
        }
    }

    public void actionPerformed(ActionEvent e) // refreshes model
    {
        G1.refreshVectorField();
        G2.refreshVectorField();
        G3.refreshVectorField();
        G1.refreshObjects();
        G2.refreshObjects();
        G3.refreshObjects();

    }

}

和第二课

package gravitationalmodel;

import static gravitationalmodel.GravitationalModel.xArray;
import static gravitationalmodel.GravitationalModel.yArray;
import static gravitationalmodel.GravitationalModel.gravConst;
import static gravitationalmodel.GravitationalModel.refreshRate;

public class GravitationalObject {
    private double xPos; // location and speed of gravitational object
    private double yPos;
    private double vX;
    private double vY;
    private double mass;

    public GravitationalObject(double x, double y, double xv, double yv,
            double m) {
        xPos = x;
        yPos = y;
        vX = xv;
        vY = yv;
        mass = m;
    }

    public void refreshVectorField() // calculates gravitational field
    {
        int k = 1;
        for (int x = 0; x < 1920; ++x) {
            if (xPos > x)
                k = 1;
            else
                k = -1;
            if (xPos - x == 0)
                ++x;
            xArray[x] += k * (gravConst * mass) / Math.pow(xPos - x, 2.0); // errors
                                                                            // on
                                                                            // this
                                                                            // line
        }
        for (int y = 0; y < 1200; ++y) {
            if (yPos < y)
                k = 1;
            else
                k = -1;
            yArray[y] += (gravConst * mass) / Math.pow(Math.abs(yPos - y), 2); // errors
                                                                                // on
                                                                                // this
                                                                                // line
        }
    }

    public void refreshObjects() {
        vX += refreshRate / 1000 * xArray[(int)xPos]; // errors on these lines
        vY += refreshRate / 1000 * yArray[(int)yPos];
        xPos += refreshRate / 1000 * vX;
        xPos += refreshRate / 1000 * vX;
    }
}

在不同的类中使用公共数组

2 个答案: