我最终决定为我的记忆游戏制作出真正的游戏零件，并且再次出现空指针异常错误。之前我已经在这里问过同样的问题，所以很抱歉这是否属于垃圾邮件，但是我根本无法弄清楚问题出在哪里！
是的，我是编程新手，所以对为什么您必须做“在此处插入答案”做一点解释将对您大有帮助！
现在这是我的Square班级（这些是您必须记住的正方形以及游戏的起点）：
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();
}
}
}
这是我的NormalMode类（在这里我从正方形调用方法并渲染事物）：
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;
}
}
我也在使用精彩的Slick2D库！如果只有更好的文档。
错误：
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)
最佳答案
您永远不会在gameStarter中初始化NormalMode，因此，当您尝试在gameStarter.startGame(g);中调用NormalMode#init()时，您试图在一个空对象上执行一个方法。
实际上，您有很多地方未能初始化字段：
类game中的Square（在game.wait(5000);中调用Square#startGame()）
类g中的NormalMode（传递给使用它的Square#startGame()）