Астероид игра NullPointerException error

Question

У меня возникли серьезные проблемы с моей игрой астероидов. Я пытаюсь вызвать мой метод Game.java run() в моем основном методе в Asteroid.java, но я получаю ту же ошибку:

Exception in thread "main" java.lang.NullPointerException 
at asteroids.Asteroids.main(Asteroids.java:15) 
Java Result: 1 

Может кто-то помочь мне понять, почему это происходит?

вот мой код:

Asteroids.java

package asteroids; 
import java.applet.*; 

import java.awt.*; 
import java.awt.event.*; 
import java.awt.geom.Point2D; 
import java.util.ArrayList; 
import java.io.IOException; 

@SuppressWarnings("serial") 
public class Asteroids { 

    Game game = null; 
    public static void main(String[] args){ 
     new Asteroids().game.run(); 
    } 
} 

// NEW Game.java //

пакет астероиды;

import java.applet.*; 

import java.awt.*; 
import java.awt.event.*; 
import java.awt.geom.Point2D; 
import java.util.ArrayList; 

//@SuppressWarnings("serial") 
public class Game extends Applet implements Runnable, KeyListener { 

     //timing variables 
     Thread thread; 
     long startTime, endTime, framePeriod; 

     //graphics variables 
     Image img; 
     Dimension dim; 
     int width, height; 
     Graphics g; 

     //text items 
     int level, lives, score; 

     SpaceShip ship; 
     boolean shipCollision, shipExplode; 

     //ArrayList to hold asteroids 
     ArrayList<Asteroid> asteroids = new ArrayList<>(); 
     int numOfAsteroids = 1; 

     //ArrayList to hold the lasers 
     ArrayList<Laser> lasers = new ArrayList<>(); 
     final double rateOfFire = 10; //limits rate of fire 
     double rateOfFireRemaining; //decrements rate of fire 

     //ArrayList to hold explosion particles 
     ArrayList<AsteroidExplosion> explodingLines = new ArrayList<>(); 

     //ArrayList to hold ship explosions 
     ArrayList<ShipExplosion> shipExplosion = new ArrayList<>(); 
     public void Game() 
     { 
      init(); 

     } 
     public void init() { 
       resize(900,700); //set size of the applet 
       dim = getSize(); //get dimension of the applet 
       width = dim.width; 
       height = dim.height; 
       framePeriod = 25; //set refresh rate 

       addKeyListener(this); //to get commands from keyboard 
       setFocusable(true); 

       ship = new SpaceShip(width/2, height/2, 0, .15, .5, .15, .98); //add ship to game 
       shipCollision = false; 
       shipExplode = false; 
       level = numOfAsteroids; 
       lives = 3; 
       addAsteroids(); 


       img = createImage(width, height); //create an off-screen image for double-buffering 
       g = img.getGraphics(); //assign the off-screen image 
       thread = new Thread(this); 
       thread.start(); 
     } 

     @Override 
     public void paint(Graphics gfx) { 
       Graphics2D g2d = (Graphics2D) g; 
     //give the graphics smooth edges 
     RenderingHints rh = new RenderingHints(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); 
     rh.put(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY); 
     g2d.setRenderingHints(rh); 

     g2d.setColor(Color.BLACK); 
     g2d.fillRect(0, 0, width, height); //add a black background 

     //add text for lives, score, and level 
     g2d.setColor(Color.WHITE); 
     g2d.drawString("Level : " + level, 10, 690); 
     g2d.drawString("Lives : " + lives, 110, 690); 
     g2d.drawString("Score : " + score, 210, 690); 



     for(Asteroid a: asteroids) { //draw asteroids 
       a.draw(g2d); 
     } 

     for(Laser l : lasers) { //draw lasers 
       l.draw(g2d); 
     } 

     for(AsteroidExplosion e : explodingLines) { 
       e.draw(g2d); 
     } 

     for(ShipExplosion ex : shipExplosion) 
       ex.draw(g2d); 

     ship.draw(g2d); //draw ship 
     if(shipCollision) { 
       shipExplosion.add(new ShipExplosion(ship.getX(), ship.getY(), 10, 10)); 
         ship.setX(width/2); 
         ship.setY(height/2); 
         shipCollision = false; 
         lives--; 
     } 

     gfx.drawImage(img, 0, 0, this); //draw the off-screen image (double-buffering) onto the applet 
     } 

     @Override 
     public void update(Graphics gfx) { 
       paint(gfx); //gets rid of white flickering 
     } 

     @Override 
     public void run(){ 
       for(; ;) { 
         startTime = System.currentTimeMillis(); //timestamp 
         ship.move(width, height);      //ship movement 
         for(Asteroid a : asteroids) {   //asteroid movement 
           a.move(width, height); 
         } 
         for(Laser l : lasers) {       //laser movement 
           l.move(width, height); 
         } 
         for(int i = 0 ; i<lasers.size() ; i++) {  //laser removal 
           if(!lasers.get(i).getActive()) 
             lasers.remove(i); 
         } 
         for(AsteroidExplosion e : explodingLines) {      //asteroid explosion floating lines movement 
           e.move(); 
         } 
         for(int i = 0 ; i<explodingLines.size(); i++) {   //asteroid explosion floating lines removal 
           if(explodingLines.get(i).getLifeLeft() <= 0) 
             explodingLines.remove(i); 
         } 
         for(ShipExplosion ex : shipExplosion){ //ship explosion expansion 
           ex.expand(); 
         } 
         for(int i = 0 ; i<shipExplosion.size() ; i++) {   
           if(shipExplosion.get(i).getLifeLeft() <= 0) 
             shipExplosion.remove(i); 
         } 
         rateOfFireRemaining--; 
         collisionCheck(); 
         if(asteroids.isEmpty()) { 
           numOfAsteroids++; 
           addAsteroids(); 
           level = numOfAsteroids; 
         } 
         repaint(); 
         try { 
           endTime = System.currentTimeMillis(); //new timestamp 
           if(framePeriod - (endTime-startTime) > 0)        //if there is time left over after repaint, then sleep 
             Thread.sleep(framePeriod - (endTime - startTime));  //for whatever is remaining in framePeriod 
         } catch(InterruptedException e) {} 
       } 
     } 

     @Override 
     public void keyPressed(KeyEvent e) { 
       int key = e.getKeyCode(); 
       //fires laser 
       if(key == KeyEvent.VK_SPACE) { 
         if(rateOfFireRemaining <= 0) { 
           lasers.add(ship.fire()); 
           rateOfFireRemaining = rateOfFire; 
         } 
       } 
       if(key == KeyEvent.VK_UP) 
         ship.setAccelerating(true); 
       if(key == KeyEvent.VK_RIGHT) 
         ship.setTurningRight(true); 
       if(key == KeyEvent.VK_LEFT) 
         ship.setTurningLeft(true); 
       if(key == KeyEvent.VK_DOWN) 
         ship.setDecelerating(true); 
     } 

     @Override 
     public void keyReleased(KeyEvent e) { 
       int key = e.getKeyCode(); 
       if(key == KeyEvent.VK_UP) 
         ship.setAccelerating(false); 
       if(key == KeyEvent.VK_RIGHT) 
         ship.setTurningRight(false); 
       if(key == KeyEvent.VK_LEFT) 
         ship.setTurningLeft(false); 
       if(key == KeyEvent.VK_DOWN) 
         ship.setDecelerating(false); 
     } 

     @Override 
     public void keyTyped(KeyEvent e) { 

     } 

     public void addAsteroids() { 
       int numAsteroidsLeft = numOfAsteroids; 
       int size; 

       for(int i=0 ; i<numOfAsteroids ; i++) {   //add asteroids to game 
         //randomize starting position 
         int asteroidX = (int)(Math.random() * width) + 1; 
         int asteroidY = (int)(Math.random() * height) + 1; 

         //randomize speed and direction 
         double xVelocity = Math.random() + 1; //horizontal velocity 
        double yVelocity = Math.random() + 1; //vertical velocity 
        //used starting direction 
        int xDirection = (int)(Math.random() * 2); 
        int yDirection = (int)(Math.random() * 2); 
         //randomize horizontal direction 
         if (xDirection == 1) 
           xVelocity *= (-1); 
         //randomize vertical direction 
         if (yDirection == 1) 
           yVelocity *= (-1); 

        //if there are more then four asteroids, any new ones are MEGA asteroids 
        if(numAsteroidsLeft > 4) { 
         size = 2; 
        } else { size = 1; 
        } 

         asteroids.add(new Asteroid(size, asteroidX, asteroidY, 0, .1, xVelocity, yVelocity)); 
         numAsteroidsLeft--; 

         //Make sure that no asteroids can appear right on top of the ship 
           //get center of recently created asteroid and ship and check the distance between them 
           Point2D asteroidCenter = asteroids.get(i).getCenter(); 
           Point2D shipCenter = ship.getCenter(); 
           double distanceBetween = asteroidCenter.distance(shipCenter); 

           //if asteroid center is within 80 pixels of ship's center, remove it from the ArrayList and rebuild it 
           if(distanceBetween <= 80) { 
             asteroids.remove(i); 
             i--; 
             numAsteroidsLeft++; 
           } 

       } 
     } 

     public void collisionCheck() { 
       //cycle through active asteroids checking for collisions 
       for(int i = 0 ; i < asteroids.size() ; i++) { 
         Asteroid a = asteroids.get(i); 
         Point2D aCenter = a.getCenter(); 

         //check for collisions between lasers and asteroids 
         for(int j = 0 ; j < lasers.size() ; j++) { 
           Laser l = lasers.get(j); 
           Point2D lCenter = l.getCenter(); 

           double distanceBetween = aCenter.distance(lCenter); 
           if(distanceBetween <= (a.getRadius() + l.getRadius())) { 

             //split larger asteroids into smaller ones, remove smaller asteroids from screen 
             if(a.getRadius() >= 60) { 
               for(int k = 0 ; k < 3 ; k++) 
                 explodingLines.add(a.explode()); 
               split(i); 
               score += 200; 
             } else if(a.getRadius() >= 30){ 
               for(int k = 0 ; k < 3 ; k++) 
                 explodingLines.add(a.explode()); 
               split(i); 
               score += 100; 
             } else { 
               for(int k = 0 ; k < 3 ; k++) 
                 explodingLines.add(a.explode()); 
               asteroids.remove(i); 
               score += 50; 
             } 

             lasers.remove(j); //remove laser from screen 
           } 
         } 

         //check for collisions between ship and asteroid 
         Point2D sCenter = ship.getCenter(); 
         double distanceBetween = aCenter.distance(sCenter); 
         if(distanceBetween <= (a.getRadius() + ship.getRadius())) { 
           shipCollision = true; 
           shipExplode = true; 
         } 
       } 
     } 

     public void split(int i) { 
       Asteroid a = asteroids.get(i); 
       double bigAsteroidX = a.getX(); 
       double bigAsteroidY = a.getY(); 
       int size = (a.getSize()/2); 
       asteroids.remove(i); 
       for(int j = 0 ; j<2 ; j++) { 
         //randomize speed and direction 
         double xVelocity = Math.random() + 1; //horizontal velocity 
        double yVelocity = Math.random() + 1; //vertical velocity 
        //used randomize starting direction 
        int xDirection = (int)(Math.random() * 2); 
        int yDirection = (int)(Math.random() * 2); 
         //randomize horizontal direction 
         if (xDirection == 1) 
           xVelocity *= (-1); 
         //randomize vertical direction 
         if (yDirection == 1) 
           yVelocity *= (-1); 
         asteroids.add(new Asteroid(size, bigAsteroidX, bigAsteroidY, 0, .1, xVelocity, yVelocity)); 
       } 


     } 
} 

// Edit Update // Хорошо, я попробовал много вещей, и обнаружил, что несмотря на то, что игра работает, когда я отладки Game.java и она не работает, когда я запускаю его через астероиды. Ява. Я обнаружил, что img = createIimg = createImage (ширина, высота); и g = img.getGraphics(); возвращают значение null и что GraphicsEnvironment.isHeadless() возвращает true. Как мне изменить свою проблему, чтобы исправить эту проблему?

Ошибка

Exception in thread "main" java.lang.NullPointerException 
    at asteroids.Game.init(Game.java:67) 
    at asteroids.Game.Game(Game.java:45) 
    at asteroids.Asteroids.main(Asteroids.java:15) 
Java Result: 1 

Answer 1

Эта вещь является недействительным.

new Asteroids().game 

Именно поэтому вы получаете это исключение NullPointerException, когда вы вызываете его.

Answer 2

Game game = null; 
public static void main(String[] args){ 
    new Asteroids().game.run();   
} 

Программа работает от метода main. game - null.

Может быть, вы должны иметь

Game game = new Game(); // instead of null 

Answer 3

Попробуйте это может быть помочь

Game game = null; 
public static void main(String[] args){ 
If(Asteroids().game != null){ 
    new Asteroids().game.run(); 
}  
} 

Answer 4

У вас есть переменная «игра» нулевая, и вы пытались вызвать метод «запустить» на этом варе (game.run); очевидно, если «игра» равна нулю, вы не можете получить этот метод и выбрасываете исключение nullpointer.

Game game=new Game(); 

это все, что вам нужно. Ваш окончательный код:

Game game = new Game();//<----- here is the change 
public static void main(String[] args){ 
    new Asteroids().game.run(); 
}