我正在学习Java游戏开发教程的一系列教程。如果有帮助的话，我已经从新浪那里获得了Java的基本知识。无论如何，我被困在这个教程上：http://www.youtube.com/watch?v=hN1v1ZhITDc&feature=c4-overview-vl&list=PL54DB126285ED0420我为本教程创建的程序有点像2D Minecraft，此时，程序应该显示一个窗口，上面有几块泥土，石头和天空按特定顺序排列。当我运行它时，它只显示一个空白的JFrame，我得到这些错误：
at mineGameMain.World.draw(World.java:80)
at mineGameMain.GamePanel.draw(GamePanel.java:91)
at mineGameMain.GamePanel.gameRender(GamePanel.java:85)
at mineGameMain.GamePanel.run(GamePanel.java:51)
at java.lang.Thread.run(Unknown Source)
我有三个班级，主要：
package mineGameMain;
import javax.swing.JFrame;
public class Main extends JFrame{
GamePanel gp;
public Main(){
gp = new GamePanel();
setSize(500, 400);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setVisible(true);
setResizable(false);
add(gp);
}
public static void main(String[] args){
Main m = new Main();
}
}
的GamePanel：
package mineGameMain;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class GamePanel extends JPanel implements Runnable{
//Double Buffering
private Image dbImage;
private Graphics dbg;
//JPanel variables
static final int GWIDTH = 500, GHEIGHT = 400;
static final Dimension gameDim = new Dimension(GWIDTH, GHEIGHT);
//Game Variables
private Thread game;
private volatile boolean running = false;
//Game Objects
World world;
public GamePanel(){
world = new World();
setPreferredSize(gameDim);
setBackground(Color.WHITE);
setFocusable(true);
requestFocus();
//Handle all key inputs
addKeyListener(new KeyAdapter(){
public void keyPressed(KeyEvent e){
}
public void keyReleased(KeyEvent e){
}
public void Typed(KeyEvent e){
}
});
}
public void run(){
while(running){
gameUpdate();
gameRender();
paintScreen();
}
}
private void gameUpdate(){
if(running && game != null){
//Update game state
}
}
private void gameRender(){
if(dbImage == null){
dbImage = createImage(GWIDTH, GHEIGHT);
if(dbImage == null){
System.err.println("dbImage IS STILL NULL SO SHUTUPBEQUIET!");
return;
}else{
dbg = dbImage.getGraphics();
}
}
//Clear the screen
dbg.setColor(Color.WHITE);
dbg.fillRect(0, 0, GWIDTH, GHEIGHT);
//draw Game Methods
draw(dbg);
}
/*Draw all game content in this method*/
private void draw(Graphics g) {
world.draw(g);
}
private void paintScreen(){
Graphics g;
try{
g = this.getGraphics();
if(dbImage != null && g != null){
g.drawImage(dbImage, 0, 0, null);
}
Toolkit.getDefaultToolkit().sync();
}catch(Exception e){
System.err.println(e);
}
}
public void addNotify(){
super.addNotify();
startGame();
}
private void startGame(){
if(game == null || !running){
game = new Thread(this);
game.start();
running = true;
}
}
public void stopGame(){
if(running){
running = false;
}
}
private void log(String s){
System.out.println(s);
}
}
最后，世界：
package mineGameMain;
import java.awt.Image;
import java.awt.*;
import javax.swing.ImageIcon;
public class World {
private Rectangle[] blocks;
private Image[] blockImg;
private final int arrayNum = 500;
//Block images
private Image BLOCK_DIRT_TOP, BLOCK_DIRT, BLOCK_STONE, BLOCK_SKY;
private int x, y;
public World(){
BLOCK_DIRT_TOP = new ImageIcon("/MineGame/src/mineGameMain/Tile_Grass.png").getImage();
BLOCK_DIRT = new ImageIcon("/MineGame/src/mineGameMain/Tile_Dirt.png").getImage();
BLOCK_STONE = new ImageIcon("/MineGame/src/mineGameMain/Tile_Stone.png").getImage();
BLOCK_STONE = new ImageIcon("/MineGame/src/mineGameMain/Tile_Sky.png").getImage();
blocks = new Rectangle[500];
blockImg = new Image[500];
loadArrays();
}
private void loadArrays(){
for(int i = 0; i < arrayNum; i++){
if(x >= 500){
x = 0;
y += 20;
}
if( i >= 0 && i < 100){
blockImg[i] = BLOCK_SKY;
blocks[i] = new Rectangle(x, y, 20, 20);
}
if( i >= 100 && i < 120){
blockImg[i] = BLOCK_DIRT_TOP;
blocks[i] = new Rectangle(x, y, 20, 20);
}
if( i >= 125 && i < 220){
blockImg[i] = BLOCK_DIRT;
blocks[i] = new Rectangle(x, y, 20, 20);
}
if( i >= 225 && i < 500){
blockImg[i] = BLOCK_STONE;
blocks[i] = new Rectangle(x, y, 20, 20);
}
x += 20;
}
}
public void draw(Graphics g){
for(int i = 0; i < arrayNum; i++){
g.drawImage(blockImg[i], blocks[i].x, blocks[i].y, null);
}
}
}
感谢您的时间。如果我发布了这个错误或者我遗漏了任何细节，请告诉我。
答案 0 :(得分：1)
在下面找到一种方法可以将您的问题转换为SSCCE（实际上它是一个固定版本）
你的代码中应该避免一些错误
invokeLater paintComponent并在需要时调用repaint()。getGraphics上使用JComponent，始终将Graphics个对象作为方法参数提供（例如在paintComponent中）。JFrame - ＆gt;如果您不需要（不实际向JFrame添加行为）setVisible(true)作为JFrame的最后陈述。draw方法中导致NullPointerException（这可能是您的错误的根源）。// this is line 80 of the World class之类的评论来确定您的行号，import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Rectangle;
import java.net.MalformedURLException;
import java.net.URL;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class Main extends JFrame {
GamePanel gp;
public Main() throws MalformedURLException {
gp = new GamePanel();
setSize(500, 400);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
add(gp);
pack();
setVisible(true);
}
public static class World {
private Rectangle[] blocks;
private Image[] blockImg;
private final int arrayNum = 500;
// Block images
private Image BLOCK_DIRT_TOP, BLOCK_DIRT, BLOCK_STONE, BLOCK_SKY;
private int x, y;
public World() throws MalformedURLException {
BLOCK_DIRT_TOP = new ImageIcon(new URL("http://i909.photobucket.com/albums/ac298/XxEnoAsaIxX/grass2test.png?t=1303852677"))
.getImage();
BLOCK_DIRT = new ImageIcon(new URL(
"http://i909.photobucket.com/albums/ac298/XxEnoAsaIxX/sparsedirtandgrasstile.png?t=1300172998")).getImage();
BLOCK_STONE = new ImageIcon(new URL("http://www.stonetilesupply.com/v/vspfiles/photos/MARBL-BTTCNCLASSICO-2S.jpg")).getImage();
BLOCK_SKY = new ImageIcon(new URL("http://lacoste.scene7.com/is/image/lacoste/swatch_10_CH0783-00_SVH_24?$swatch$")).getImage();
blocks = new Rectangle[500];
blockImg = new Image[500];
loadArrays();
}
private void loadArrays() {
for (int i = 0; i < arrayNum; i++) {
if (x >= 500) {
x = 0;
y += 20;
}
if (i >= 0 && i < 100) {
blockImg[i] = BLOCK_SKY;
blocks[i] = new Rectangle(x, y, 20, 20);
}
if (i >= 100 && i < 120) {
blockImg[i] = BLOCK_DIRT_TOP;
blocks[i] = new Rectangle(x, y, 20, 20);
}
// Here missing block for 120 to 125
if (i >= 120 && i < 125) {
blockImg[i] = BLOCK_STONE;
blocks[i] = new Rectangle(x, y, 20, 20);
}
if (i >= 125 && i < 220) {
blockImg[i] = BLOCK_DIRT;
blocks[i] = new Rectangle(x, y, 20, 20);
}
// Here missing block for 220 to 225
if (i >= 220 && i < 225) {
blockImg[i] = BLOCK_SKY;
blocks[i] = new Rectangle(x, y, 20, 20);
}
if (i >= 225 && i < 500) {
blockImg[i] = BLOCK_STONE;
blocks[i] = new Rectangle(x, y, 20, 20);
}
x += 20;
}
}
public void draw(Graphics g) {
for (int i = 0; i < arrayNum; i++) {
g.drawImage(blockImg[i], blocks[i].x, blocks[i].y, null);
}
}
}
public static class GamePanel extends JPanel {
// JPanel variables
// Game Objects
World world;
public GamePanel() throws MalformedURLException {
world = new World();
setPreferredSize(new Dimension(500, 400));
setBackground(Color.WHITE);
setFocusable(true);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
world.draw(g);
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
try {
new Main();
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
}
}