Java 空指针异常错误，我们再次见面

我最终决定为我的记忆游戏制作实际的游戏部分，我再次得到了空指针异常错误。我以前在这里也问过同样的问题，所以如果这算是垃圾邮件，我很抱歉，但我根本不知道问题出在哪里

是的，我是编程新手，所以解释一下为什么要在这里插入答案将是一个很大的帮助

现在是我的方块课（这些是你必须记住的方块，以及游戏从哪里开始）：

这是我的NormalMode类（在这里我从square和render调用方法）：

---

您从未在

NormalMode

中初始化

gameStarter

，因此当您尝试调用

gameStarter.startGame（g）时

在

NormalMode#init（）

中，您正试图对空对象执行一个方法

实际上，您有很多地方无法初始化字段：

• game

  在类中

  Square

  （调用

  game.wait（5000）；

  在

  Square#startGame（）中）

• 类

  NormalMode

  中的

  g

  （传递到使用它的

  Square#startGame（）

  ）

---

您需要将

gameStarter

设置为某个值。当前，您将其保留为null。

在我的记事本应用程序中，发生此异常是因为我指向一个未初始化的变量。。。所以你需要初始化gamestarter。。。希望它能起作用：）

你能发一个stacktrace吗？是的，对不起，我以为我把它放进去了！我做到了这一点，但我仍然在org.newdawn.slick.state.StateBasedGame.init的data.src.Square.startGame（Square.java:115）处的data.src.NormalMode.init（NormalMode.java:23）处的org.newdawn.slick.state.StateBasedGame.init（StateBasedGame.java:171）处的线程“main”java.lang.nullpointerexception中得到了nullpointerexception错误（ScalableGame.java:69）在org.newdawn.slick.AppGameContainer.setup（AppGameContainer.java:393）在org.newdawn.slick.AppGameContainer.start（AppGameContainer.java:317）在data.src.Core.main（Core.java:30）上@波克先生，我已经更新了我的答案，以反映您未能初始化的另外两个位置。那么，您如何初始化图形上下文？我无法理解这一点。另外，我如何初始化gameStarter？我认为只需执行“gameStarter=new Square（arg0）”即可有什么诀窍吗？@MrPork这是你的应用程序，我不知道如何初始化你所有的自定义类。就

Graphics

而言，我想你应该是从这个代码上游的某个地方继承的。我有，但它仍然给我同样的错误，我更新了普通模式类。你仍然有问题吗？？

package data.src;

import java.util.Random;

import org.newdawn.slick.Color;
import org.newdawn.slick.GameContainer;
import org.newdawn.slick.Graphics;
import org.newdawn.slick.Image;
import org.newdawn.slick.SlickException;
import org.newdawn.slick.state.StateBasedGame;

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) {
                container.getGraphics();

    }

    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);

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

        }
    }

    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();
            }
        }
    }

    //Normal mode Methods begin here. Ends at EndGame().
    public void  startGame(Graphics g) throws SlickException {

        g.setColor(Color.red);
        g.drawString("Remember the squares! The game starts in 5 seconds!", 300, 200);
        clickable = false;
        started = false;
        try {
            game.wait(5000);
            started = true;
            clickable = true;
            returnNumberOfSquares();
            squareCorrect = new Image("res/squareIncorrect");
        }
        catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

package data.src;

import org.newdawn.slick.GameContainer;
import org.newdawn.slick.Graphics;
import org.newdawn.slick.SlickException;
import org.newdawn.slick.state.BasicGameState;
import org.newdawn.slick.state.StateBasedGame;

public class NormalMode extends BasicGameState {

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

    public NormalMode() {

    }

    @Override
    public void init(GameContainer arg0, StateBasedGame Game)throws SlickException {
        gameStarter = new Square(arg0);
        gameStarter.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;
    }
}

Exception in thread "main" java.lang.NullPointerException
    at data.src.NormalMode.init(NormalMode.java:22)
    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)