Java swing二維重力模擬不起作用

Question

我有一個重力模擬的代碼，玩家可以按住鼠標點擊創建行星（鼠標按下的時間越長，它越大）到100顆行星。

但我的問題是，行星是成功創建，但沒有顯示。

代碼：

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(); 
    } 
} 

感謝您的幫助。

Answer 1

在您的for-each循環中，您將分配一個新的Planet到本地變量planeti（for-each循環的本地，之後丟棄），所以這沒用。

您應該將此循環替換爲for循環，以便您可以將Planet分配給陣列的當前索引。這種循環

  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; 
       } 
     } 

：

所以更換這個循環

 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; 
       } 
     }