Question

我刚才问了同样的问题，我被告知初始化我的squareChecker变量，所以我做了。由于某些我不知道的原因，我仍然会得到同样的错误。我整天都花了很多时间试图自己解决这个问题，但无济于事。有谁知道我的问题是什么？

我的普通模式类（我从方形类中调用方法并渲染事物）：

public class NormalMode extends BasicGameState {

    private Square[][] square = new Square[4][4];
    private Square squareChecker;
    Graphics g;

    public NormalMode() { }

    @Override
    public void init(GameContainer arg0, StateBasedGame Game)throws SlickException {
        squareChecker = new Square(arg0);
        squareChecker.startGame(g);
        for(int i = 0; i < square.length; i++){
            for(int j = 0; j < square.length; j++){
                square[i][j] = new Square(arg0);
                square[i][j].createRandom();
            }
        }   
    }

    @Override
    public void render(GameContainer container, StateBasedGame game, Graphics g)
                       throws SlickException{

        square[0][0].squareDraw(100, 300, g);
        square[0][1].squareDraw(150, 300, g);
        square[0][2].squareDraw(200, 300, g);
        square[0][3].squareDraw(250, 300, g);

        square[1][0].squareDraw(100, 400, g);
        square[1][1].squareDraw(150, 400, g);
        square[1][2].squareDraw(200, 400, g);
        square[1][3].squareDraw(250, 400, g);

        square[2][0].squareDraw(100, 500, g);
        square[2][1].squareDraw(150, 500, g);
        square[2][2].squareDraw(200, 500, g);
        square[2][3].squareDraw(250, 500, g);

        square[3][0].squareDraw(100, 600, g);
        square[3][1].squareDraw(150, 600, g);
        square[3][2].squareDraw(200, 600, g);
        square[3][3].squareDraw(250, 600, g);                   
    }

    @Override
    public void update(GameContainer container, StateBasedGame game, int delta)
                       throws SlickException { }

    @Override
    public int getID() {
        return 3;
    }   
}

我的广场班：

public class Square {

    private StateBasedGame game;
    boolean correct;
    boolean clickable;
    boolean clicked;
    boolean started;
    int squares;
    int squareX;
    int squareY;
    public Image squareIncorrect;
    public Image squareCorrect;

    //For drawing these images from other classes
    {
        try {
            squareIncorrect = new Image("res/squareIncorrect.png");
        } catch (SlickException e1) {

            e1.printStackTrace();
        }
        try {
            squareCorrect =  new Image("res/squareCorrect.png");
        } catch (SlickException e) {

            e.printStackTrace();
        }
    }

    public Square(GameContainer container) { }

    public boolean checkCorrect(){
        return correct;
    }
    public boolean checkClickable(){
        return clickable;
    }

    public boolean checkClicked(){
        return clicked;
    }

    public int returnNumberOfSquares(){
        return squares;
    }
    //Draw appropriate square on screen depending on the creatRandom. CREATE THE RANDOM FIRST!
        public void squareDraw(int x ,int y, Graphics g)throws SlickException{

            if(correct == true){
                g.drawImage(squareCorrect, x, y);
                started = true;
            }
            else if(correct == false){
                g.drawImage(squareIncorrect, x, y);
            started = true;
            }
    }

    public void createRandom(){

        Random rand = new Random();
        int sRand = rand.nextInt(2);

            if(sRand == 0){
                correct = false;
                clickable = true;
                clicked = false;
                System.out.println("This square is a phony!");
            }
            else if(sRand == 1){
                correct = true;
                clickable = true;
                clicked = false;
                System.out.println("This is a true Square!");
                squares = squares+1;
            }
        }


    public void youWin(int x, int y, Graphics g){
        if(squares == 0){
            g.drawString("You win!", x, y);
            try {
                wait(4000);
                game.enterState(0);
            } catch (InterruptedException e) {
                e.printStackTrace();
      }
    }
  }

    public void startGame(Graphics g){
        g.drawString("Remember the blue squares! The game will start in 5 seconds!", 200, 300);

    }
}

这是我得到的错误：

Exception in thread "main" java.lang.NullPointerException
    at data.src.Square.startGame(Square.java:112)
    at data.src.NormalMode.init(NormalMode.java:23)
    at org.newdawn.slick.state.StateBasedGame.init(StateBasedGame.java:171)
    at org.newdawn.slick.ScalableGame.init(ScalableGame.java:69)
    at org.newdawn.slick.AppGameContainer.setup(AppGameContainer.java:393)
    at org.newdawn.slick.AppGameContainer.start(AppGameContainer.java:317)
    at data.src.Core.main(Core.java:30)

Answer 1

在NormalMode.Init()中，您拨打squareChecker.startGame(g);

g定义为Graphics g;。

startGame()来电g.drawString()。

这使我得出结论，在将g传递给startGame()方法之前，您不会将其{{1}}实例化。

空指针异常再一次

1 个答案: