Java Swing 2D重力仿真不起作用

Question

我有这段代码用于重力模拟，玩家可以按住鼠标单击以在最多100个行星的鼠标位置上按住鼠标来创建行星（按住鼠标的时间越长，它越大）。

但是我的问题是，成功创建了行星，但是没有显示出来。

代码：

import javax.swing.JFrame;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.image.BufferedImage;
import java.io.*;
import javax.imageio.ImageIO;
import javax.swing.JPanel;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.Random;
import java.util.Arrays;
import java.awt.EventQueue;
import javax.swing.JFrame;
import java.awt.Point;
import java.awt.event.MouseWheelEvent;
import java.awt.event.MouseWheelListener;

class Planet {
     public float x;
     public float y;
     public float w;
     public float xv;
     public float yv;
     public Planet(float xn,float yn,float wn,float xvn,float yvn) {
         x=xn;
         y=yn;
         w=wn;
         yv=yvn;
         xv=xvn;
     }
     public float distance(Planet planet) {
         float xdis=x-planet.x;
         float ydis=y-planet.y;
         return (float)Math.sqrt((xdis*xdis)+(ydis*ydis));
     }
     public void move() {
         x=x+xv;
         y=y+yv;
     }
     public void gravity(Planet[] objects,float intensity) {
         Planet planet;
         float distancec;
         float gravity;
         for (Planet obj:objects) {
              if (obj != null) {
                  if (obj.equals(this)==false) {
                      planet=obj;
                      distancec=distance(planet);
                      gravity=distancec*(planet.w/intensity);
                      xv=xv+((x-planet.x)*gravity);
                      yv=yv+((y-planet.y)*gravity);
                      if (distancec < w+planet.w) {
                          //Probably bump off or unite...
                      }
                  }
              }
              else {
                  break;
              }
         }
     }
}
public class Gravity extends JFrame implements MouseListener, KeyListener, MouseWheelListener {
     public int[] mouse=new int[5];
     public Planet[] planets=new Planet[100];
     public void mousePressed(MouseEvent m) {
         if (m.getButton() == m.BUTTON1) {
             mouse[2]=1;
         }
         if (m.getButton() == m.BUTTON1) {
             mouse[4]=1;
         }
    }
    public void mouseClicked(MouseEvent m) {
         if (m.getButton() == m.BUTTON1) {
             mouse[2]=3;
         }
         if (m.getButton() == m.BUTTON1) {
             mouse[4]=3;
         }
    }
    public void mouseReleased(MouseEvent m) {
         if (m.getButton() == m.BUTTON1) {
             mouse[2]=2;
         }
         if (m.getButton() == m.BUTTON1) {
             mouse[4]=2;
         }
    }
    public void mouseEntered(MouseEvent m) {
    }
    public void mouseExited(MouseEvent m) {
    }
    public void mouseWheelMoved(MouseWheelEvent w) {
         mouse[3]=w.getWheelRotation();
    }
     public void keyTyped(KeyEvent e) {

     }
     public void keyReleased(KeyEvent e) { 

     }
     public void keyPressed(KeyEvent e) {

     } 
     public Gravity(){
          super("Gravity");
          requestFocus();
          addKeyListener(this);
          addMouseListener(this);
          setTitle("Gravitation");
          setContentPane(new Zeichenflaeche());

          setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

          setSize(800, 600);

          setResizable(true);

          setVisible(true); 
          while (true){
              repaint();
              try {
              Thread.sleep(33);
              } catch(InterruptedException bug) {
              Thread.currentThread().interrupt();
              System.out.println(bug);
              }
              mouse[0]=MouseInfo.getPointerInfo().getLocation().x-getComponents()[0].getLocationOnScreen().x;
              mouse[1]=MouseInfo.getPointerInfo().getLocation().y-getComponents()[0].getLocationOnScreen().y;
              repaint();
          }
     }


     class Zeichenflaeche extends JPanel{
        public boolean dragging;
        public float w;
        public Zeichenflaeche() {
        }
        public void reset_mouse_state() {
         mouse[2]=0;
         mouse[3]=0;
         mouse[4]=0;
        }
        public void paintComponent(Graphics g){

             if (mouse[2]==1) {

                 dragging=true;
             }
             if (dragging==true) {
                 w++;
             }
             if (mouse[2]==2 || mouse[2]==3) {
                 dragging=false;
                 System.out.println("Append Planet");
                 for (Planet planeti:planets) {
                      if (planeti == null) {
                          planeti=new Planet(mouse[0],mouse[1],w,0,0);
                          System.out.println("Planet succesfully appended");
                          System.out.println(Arrays.toString(new float[] {planeti.x,planeti.y,planeti.w}));
                          break;
                      }
                 }
                 w=1;
             }
         for (Planet planeti:planets) {
              try {
                  g.setColor(Color.GREEN);
                  g.fillOval((int)planeti.x-(int)planeti.w,(int)planeti.y-(int)planeti.w,(int)planeti.w*2,(int)planeti.w*2);
                  planeti.gravity(planets,10);
                  planeti.move();
              }
              catch (Exception bug) {
              }
         }
         reset_mouse_state();
        }   
     }
     public static void main(String args[]){
            new Gravity();
     }
}

谢谢你的帮助。

Answer 1

在for-each循环中，您正在将新Planet分配给局部变量planeti （对于for-each循环是局部变量，此后被丢弃），因此这没有用。

您应该将此循环替换for循环，以便可以将Planet分配给数组的当前索引。

因此，请替换此循环：

         for (Planet planeti:planets) {
              if (planeti == null) {
                  planeti=new Planet(mouse[0],mouse[1],w,0,0);
                  System.out.println("Planet succesfully appended");
                  System.out.println(Arrays.toString(new float[] {planeti.x,planeti.y,planeti.w}));
                  break;
              }
         }

用这个循环：

        for (int i=0;i<planets.length;i++) {

              Planet currentPlanet = planets[i];

              if (currentPlanet == null) {

                  Planet newPlanet = new Planet(mouse[0],mouse[1],w,0,0);
                  planets[i] = newPlanet; 
                  System.out.println("Planet succesfully appended");
                  System.out.println(Arrays.toString(new float[] {newPlanet.x,newPlanet.y,newPlanet.w}));
                  break;
              }
         }