这是一场蛇游戏，我无法开始。当我尝试在Eclipse上运行它时，它一直在给我
Exception in thread "main" java.lang.NullPointerException
at Snake.createSnake(Snake.java:110)
at Snake.<init>(Snake.java:95)
at Driver.main(Driver.java:6)
我只需要有人请解释并帮我解决这个问题。我问了很多朋友，我知道没有人可以帮我解决。
public class Driver {
public static void main(String[] args) {
Snake game = new Snake();
}
}
以下是这个Snake课程。
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
@SuppressWarnings("serial")
class Snake extends JFrame implements KeyListener, Runnable{
JPanel gamePanel, scorePanel;
JButton extraFood;
JTextArea textAreaScore;
int x = 500;
int y = 250;
int minSnake = 3;
int directionx = 1;
int directiony = 0;
int speed = 50;
int difference = 0;
int oldx = 0;
int oldy = 0;
int score = 0;
boolean food = false;
boolean runLeft = false;
boolean runRight = true;
boolean runUp = true;
boolean runDown = true;
boolean bonusFlag = true;
Random ran = new Random();
JButton[] bc = new JButton[200];
int[] bx = new int[300];
int[] by = new int[300];
Thread myThread;
Point[] bp = new Point[300];
Point bonusp = new Point();
//initializing values
public void Values() {
minSnake = 3;
directionx = 10;
directiony = 0;
difference = 0;
score = 0;
food = false;
runLeft = false;
runRight = true;
runUp = true;
runDown = true;
bonusFlag = true;
}
//sets layout of game
public Snake() {
getContentPane().setBackground(Color.GRAY);
getContentPane().setLayout(null);
gamePanel = new JPanel();
gamePanel.setBackground(Color.LIGHT_GRAY);
gamePanel.setBounds(6, 6, 438, 223);
getContentPane().add(gamePanel);
gamePanel.setLayout(new GridLayout(1, 0, 0, 0));
scorePanel = new JPanel();
scorePanel.setBackground(Color.GRAY);
scorePanel.setBounds(6, 241, 438, 31);
getContentPane().add(scorePanel);
scorePanel.setLayout(null);
textAreaScore = new JTextArea("Your score is:" + score);
textAreaScore.setBackground(Color.LIGHT_GRAY);
textAreaScore.setBounds(0, 0, 303, 31);
scorePanel.add(textAreaScore);
//Exit Game button
JButton btnExitGame = new JButton("Exit Game");
btnExitGame.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
}
});
btnExitGame.setBounds(315, 0, 117, 29);
scorePanel.add(btnExitGame);
btnExitGame.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e) {
System.exit(0);
}
});
setVisible(true);
createSnake();
extraFood = new JButton();
extraFood.setEnabled(false);
addKeyListener(this);
//This starts the game
myThread = new Thread(this);
myThread.start();
}
//Creates snake
public void createSnake() {
for (int i = 0; i < 3; i++){
bc[i] = new JButton("b" + i);
bc[i].setEnabled(false);
gamePanel.add(bc[i]);
bc[i].setBounds(bx[0], by[0], 10, 10);
bx[i + 1] = bx[i] - 10;
by[i + 1] = by[i];
}
}
@SuppressWarnings("deprecation")
void reset(){
Values();
gamePanel.removeAll();
myThread.stop();
createSnake();
textAreaScore.setText("Your score is: " + score);
myThread = new Thread(this);
myThread.start();
}
//As snake eats food, it grows
void snakeGrow(){
bc[minSnake] = new JButton();
bc[minSnake].setEnabled(false);
gamePanel.add(bc[minSnake]);
int a = 10 + (10 * ran.nextInt(48));
int b = 10 + (10 * ran.nextInt(23));
bx[minSnake] = a;
by[minSnake] = b;
bc[minSnake].setBounds(a, b, 10, 10);
minSnake++;
}
//Snake moving logic
void moveForward() {
for (int i = 0; i < minSnake; i++) {
bp[i] = bc[i].getLocation();
}
bx[0] += directionx;
by[0] += directiony;
bc[0].setBounds(bx[0], by[0], 10, 10);
for (int i = 1; i < minSnake; i++) {
bc[i].setLocation(bp[i - 1]);
}
if (bx[0] == x) {
bx[0] = 10;
} else if (bx[0] == 0) {
bx[0] = x - 10;
} else if (by[0] == y) {
by[0] = 10;
} else if (by[0] == 0) {
by[0] = y - 10;
}
if (bx[0] == bx[minSnake - 1] && by[0] == by[minSnake - 1]) {
food = false;
score += 1;
textAreaScore.setText("Your score is: " + score);
if (score % 50 == 0 && bonusFlag == true) {
gamePanel.add(extraFood);
extraFood.setBounds((10 * ran.nextInt(50)), (10 * ran.nextInt(25)), 15, 15);
bonusp = extraFood.getLocation();
bonusFlag = false;
}
}
if (bonusFlag == false) {
if (bonusp.x <= bx[0] && bonusp.y <= by[0] && bonusp.x + 10 >= bx[0] && bonusp.y +
10 >= by[0]) {
gamePanel.remove(extraFood);
score += 100;
textAreaScore.setText("Your score is: " + score);
bonusFlag = true;
}
}
if (food == false) {
snakeGrow();
food = true;
} else {
bc[minSnake - 1].setBounds(bx[minSnake - 1], by[minSnake - 1], 10, 10);
}
gamePanel.repaint();
extracted();
}
@SuppressWarnings("deprecation")
private void extracted() {
show();
}
public void keyPressed(KeyEvent e) {
//Move to the left when player presses the left arrow key
if (runLeft == true && e.getKeyCode() == 37) {
directionx = -10; //Moves to the left by 10 pixels
directiony = 0;
runRight = false;
runUp = true;
runDown = true;
}
//Move up when player presses the up arrow key
if (runUp == true && e.getKeyCode() == 38) {
directionx = 0;
directiony = -10; //Moves up by 10 pixels
runDown = false;
runRight = true;
runLeft = true;
}
//Move to the right when the player presses the right arrow key
if (runRight == true && e.getKeyCode() == 39) {
directionx = +10; //Moves right by 10 pixels
directiony = 0;
runLeft = false;
runUp = true;
runDown = true;
}
//Move down when the player presses the down arrow key
if (runDown == true && e.getKeyCode() == 40) {
directionx = 0;
directiony = +10; //Moves down by 10 pixels
runUp = false;
runRight = true;
runLeft = true;
}
}
public void keyReleased(KeyEvent e) {
}
public void keyTyped(KeyEvent e) {
}
public void run() {
for (;;) {
//Moves the snake forward
moveForward();
try {
Thread.sleep(speed);
} catch (InterruptedException ie) {
}
}
}
}
答案 0 :(得分：8)
问题是你没有在构造函数中设置全局gamePanel变量只是它的本地版本。删除变量初始化前面的JPanel，它应该可以工作。
同样适用于您的scorePanel和textAreaScore变量。
答案 1 :(得分：3)
您将视图对象（即gamePanel，scorePanel，extraFood，textAreaScore）声明为类Snake的成员变量，但随后在构造函数中声明了同名的局部变量。
成员变量：
JPanel gamePanel, scorePanel;
JButton extraFood;
JTextArea textAreaScore;
局部变量：
public Snake() {
...
JPanel gamePanel = new JPanel();
...
JPanel scorePanel = new JPanel();
...
JTextArea textAreaScore = new JTextArea("Your score is:" + score);
...
更改构造函数以实例化您的成员变量，如下所示：
public Snake() {
...
this.gamePanel = new JPanel();
...
this.scorePanel = new JPanel();
...
this.textAreaScore = new JTextArea("Your score is:" + score);
...
答案 2 :(得分：3)
问题在于：
您定义了全局变量：
JPanel gamePanel, scorePanel;
JTextArea textAreaScore;
但你定义了dupplicate：
public Snake() {
JPanel gamePanel = new JPanel();
...
JPanel scorePanel = new JPanel();
...
JTextArea textAreaScore = new JTextArea("Your score is:" + score);
...
}
所以，将它们改为：
public Snake() {
gamePanel = new JPanel();
...
scorePanel = new JPanel();
...
textAreaScore = new JTextArea("Your score is:" + score);
...
}
就是这样。
答案 3 :(得分：2)
gamePanel的构造函数中的shadowing Snake。取代
JPanel gamePanel = new JPanel();
与
gamePanel = new JPanel();
变量scorePanel和textAreaScore具有相同的问题。
附带问题：
KeyListeners。它们不适用于Swing应用程序。请改用Key Bindings。