基本上，在我的 init 方法中，我创建了一个数组列表并用 wizardObjects 的新实例填充它。 wizardObjects 有 4 个适当填充的构造函数。运行 for 循环后，我什至有一个 System.out.println 来验证列表是否已填充。
我的问题是，当渲染方法、更新方法或任何其他方法启动时，arraylist 会抛出一个空指针异常。我不会在任何地方重新分配或重新初始化它。
顺便说一句，我正在使用 slick2d，但我认为这对这个问题来说并不重要。
public void init(GameContainer container) throws SlickException {
SpriteSheet spritesheet1 = new SpriteSheet("/res/mainsprites.png", 32, 32);
wizardSprite = spritesheet1.getSprite( 5,3 );
wizardXArray = new int[100];
wizardYArray = new int[100];
random = new Random();
map = new TiledMap("/res/map.tmx");
ArrayList<WizardObject> wizList = new ArrayList <WizardObject>(100);
for(int i = 0; i < 100 ;i++){
int randX = random.nextInt(100) * 32;
wizardXArray[i] = randX;
int randY = random.nextInt(100) * 32;
wizardYArray[i] = randY;
WizardObject wizardObject = new WizardObject(wizardXArray[i], wizardYArray[i], wizardSprite, map);
wizList.add(wizardObject);
}
for(int x = 0; x < 100 ;x++){
System.out.println(wizList.get(x));
System.out.println(wizList.get(x).getX() + " " + wizList.get(x).getY());
}
public void render(GameContainer container, Graphics g)
throws SlickException {
if(wizList == null ){
System.out.println("true");
}}
对于没有时间阅读所有内容的人来说，这就是代码的要点。对于那些这样做的人:
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Random;
import org.newdawn.slick.Animation;
import org.newdawn.slick.AppGameContainer;
import org.newdawn.slick.BasicGame;
import org.newdawn.slick.Color;
import org.newdawn.slick.GameContainer;
import org.newdawn.slick.Graphics;
import org.newdawn.slick.Image;
import org.newdawn.slick.Input;
import org.newdawn.slick.SlickException;
import org.newdawn.slick.SpriteSheet;
import org.newdawn.slick.particles.ParticleSystem;
import org.newdawn.slick.tiled.TiledMap;
import org.newdawn.slick.util.Log;
import org.newdawn.slick.gui.AbstractComponent;
import org.newdawn.slick.gui.ComponentListener;
import org.newdawn.slick.gui.MouseOverArea;
import org.newdawn.slick.gui.TextField;
import com.tinyline.tiny2d.i;
public class MainGameLoop extends BasicGame {
private static final int PLAYER_SIZE = 32;
private static final int TILE_SIZE = 32;
private boolean[][] blocked;
private int playerX = 50;
private int playerY = 50;
private int widthInTiles;
private int heightInTiles;
private int topOffsetInTiles;
private int [] wizardXArray;
private int [] wizardYArray;
private int leftOffsetInTiles;
private int randX;
private int randY;
private TiledMap map;
private Image wizardSprite;
private long currentTime;
private long dblUpdateTime;
private long updateTime;
private boolean isTicking = false;
private boolean isTocking = false;
private Random random;
private boolean isIntroOver = false;
private Image titleImage;
private Image[] circleImage;
private Animation circleAnim;
private SpriteSheet spritesheet1;
public int[] circleDuration = { 300, 300, 300 };
private int x = 100;
private int y = 100;
private int dx = 1;
private int dy = 1;
private int rx = 1;
private int ry = 450;
private int rdx = 1;
private int rdy = 1;
private int fx = 1;
private int fy = 450;
private int fdx = 1;
private int fdy = 1;
private int pdx = 1;
private int pdy = 1;
private int px = 1;
private int py = 450;
private int wdx = 1;
private int wdy = 1;
private int wx = 1;
private int wy = 450;
private Image image;
public Image baseBGImage;
public Image basePotionImage;
public Image[] brenImage;
public Animation brenAnim;
public int[] duration = { 300, 300, 300, 300 };
public WizardObject wizardObject;
public List<WizardObject> wizList;
private boolean isWizardDrawn;
public MainGameLoop() {
super("MainGameLoop");
}
/**
* @see org.newdawn.slick.BasicGame#init(org.newdawn.slick.GameContainer)
*/
public void init(GameContainer container) throws SlickException {
SpriteSheet spritesheet1 = new SpriteSheet("/res/mainsprites.png", 32, 32);
wizardSprite = spritesheet1.getSprite( 5,3 );
wizardXArray = new int[100];
wizardYArray = new int[100];
random = new Random();
image = new Image("/res/GreenFire.png");
map = new TiledMap("/res/map.tmx");
ArrayList<WizardObject> wizList = new ArrayList <WizardObject>(100);
for(int i = 0; i < 100 ;i++){
int randX = random.nextInt(100) * 32;
wizardXArray[i] = randX;
int randY = random.nextInt(100) * 32;
wizardYArray[i] = randY;
WizardObject wizardObject = new WizardObject(wizardXArray[i], wizardYArray[i], wizardSprite, map);
wizList.add(wizardObject);
}
for(int x = 0; x < 100 ;x++){
System.out.println(wizList.get(x));
System.out.println(wizList.get(x).getX() + " " + wizList.get(x).getY());
}
Image[] brenImage = { new Image("/res/Bren1.png"),
new Image("/res/Bren2.png"), new Image("/res/Bren4.png"),
new Image("/res/Bren7.png") };
brenAnim = new Animation(brenImage, duration, true);
// build a collision map based on tile properties in the TileD map
blocked = new boolean[map.getWidth()][map.getHeight()];
for (int x = 0; x < map.getWidth(); x++) {
for (int y = 0; y < map.getHeight(); y++) {
int tileID = map.getTileId(x, y, 0);
String value = map.getTileProperty(tileID, "blocked", "false");
if ("true".equals(value)) {
blocked[x][y] = true;
}
}
}
updateTime = System.currentTimeMillis() + 200;
dblUpdateTime = System.currentTimeMillis() + 400;
titleImage = new Image("/res/title.png");
baseBGImage = new Image("/res/baseBG.png");
basePotionImage = new Image("/res/potions.png");
Image[] circleImage = { new Image("/res/circle_f1.png"),
new Image("/res/circle_f2.png"),
new Image("/res/circle_f3.png") };
circleAnim = new Animation(circleImage, circleDuration, true);
// calculate some layout values for rendering the tilemap. How many
// tiles
// do we need to render to fill the screen in each dimension and how far
// is
// it from the center of the screen
widthInTiles = container.getWidth() / TILE_SIZE;
heightInTiles = container.getHeight() / TILE_SIZE;
topOffsetInTiles = heightInTiles / 2;
leftOffsetInTiles = widthInTiles / 2;
// system = new ParticleSystem();
// update the vector of movement based on the initial angle
Log.info("Window Dimensions in Tiles: " + widthInTiles + "x"
+ heightInTiles);
}
/**
* @see org.newdawn.slick.BasicGame#update(org.newdawn.slick.GameContainer,
* int)
*/
public void update(GameContainer container, int delta)
throws SlickException {
if (rx > container.getWidth() - brenAnim.getWidth())
rdx = -1;
if (rx < 0)
rdx = 1;
if (ry > (container.getWidth() - brenAnim.getHeight()) - 250)
rdy = -1;
if (ry < 440)
rdy = 1;
rx = rx + rdx * 3;
ry = ry + rdy;
if (fx > container.getWidth() - 1000)
fdx = -1;
if (fx < -500)
fdx = 1;
if (fy > (container.getWidth() - baseBGImage.getHeight()) - 200)
fdy = 0;
if (fy < 450)
fdy = 1;
fx = fx + fdx * 2;
fy = fy + fdy * 2;
if (px > container.getWidth() - 900)
pdx = -1;
if (px < -200)
pdx = 1;
if (py > container.getWidth() - wizardSprite.getHeight())
pdy = -1;
if (py < 430)
pdy = 1;
px = px + pdx;
py = py + pdy;
if (wx > map.getWidth())
wdx = -1;
if (wx < 0)
wdx = 1;
if (wy > map.getWidth() - wizardSprite.getHeight())
wdy = -1;
if (wy < 430)
wdy = 1;
wx = wx + wdx;
wy = wy + wdy;
currentTime = System.currentTimeMillis();
if (currentTime >= updateTime) {
isTicking = true;
updateTime = (currentTime + 200);
} else {
isTicking = false;
}
if (currentTime >= dblUpdateTime) {
isTocking = true;
dblUpdateTime = (currentTime + 400);
//System.out.println(container.getFPS());
} else {
isTocking = false;
}
if (isIntroOver == false) {
isWizardDrawn = false;
if (x > container.getWidth() - titleImage.getWidth())
dx = -1;
if (x < 0)
dx = 1;
if (y > (container.getWidth() - titleImage.getHeight()) - 350)
dy = -1;
if (y < 0)
dy = 1;
x = x + dx;
y = y + dy;
if (isTicking == true) {
// System.out.println("x = " + x);
// System.out.println("y = " + y);
for (int x = 0; x < map.getWidth(); x++) {
for (int y = 0; y < map.getHeight(); y++) {
map.setTileId(x, y, 0, random.nextInt(191));
}
}
if (container.getInput().isKeyPressed(Input.KEY_ENTER)) {
isIntroOver = true;
for (int x = 0; x < map.getWidth(); x++) {
for (int y = 0; y < map.getHeight(); y++) {
map.setTileId(x, y, 0, random.nextInt(191));
}
}
}
}
}
if (isIntroOver == true) {
if(container.getInput().isKeyPressed(Input.KEY_ENTER)){
isWizardDrawn = true;
}
if (container.getInput().isKeyDown(Input.KEY_W)) {
if (container.getInput().getMouseX() > 775) {
if (isTicking == true) {
playerX += 2;
}
}
if (container.getInput().getMouseX() < 50) {
if (isTicking == true) {
playerX -= 2;
}
}
if (container.getInput().getMouseY() < 425) {
if (isTicking == true) {
playerY -= 2;
}
}
if (container.getInput().getMouseY() > 50) {
if (isTicking == true) {
playerY += 2;
}
}
}
if (container.getInput().isMousePressed(0)) {
int mx = container.getInput().getMouseX();
int my = container.getInput().getMouseY();
// int tileIDmid = map.getTileId(mx, my, 0);
int px = playerX;
int py = playerY;
//
// map.setTileId((px + (mx / 32) - 13) , py + ((my / 32) - 10),
// 0, 3);
int clickedTile = map.getTileId((px + (mx / 32) - 13), py
+ ((my / 32) - 10), 0);
if (clickedTile > 185) {
System.out.println("true");
}
//
// System.out.println("Clicked x: " + mx + " y: " + my);
}
}
if (container.getInput().isKeyDown(Input.KEY_ESCAPE)) {
if (container.isFullscreen()) {
container.setFullscreen(false);
container.setMouseGrabbed(false);
} else {
container.exit();
}
}
if (container.getInput().isKeyDown(Input.KEY_M)) {
container.setFullscreen(true);
container.setMouseGrabbed(true);
}
}
private boolean blocked(float x, float y) {
return blocked[(int) x][(int) y];
}
private boolean tryMove(int x, int y) {
int newx = playerX + x;
int newy = playerY + y;
// first we try the real move, if that doesn't work
// we try moving on just one of the axis (X and then Y)
// this allows us to slide against edges
if (blocked(newx, newy)) {
if (blocked(newx, playerY)) {
if (blocked(playerX, newy)) {
// can't move at all!
return false;
} else {
playerY = newy;
return true;
}
} else {
playerX = newx;
return true;
}
} else {
playerX = newx;
playerY = newy;
return true;
}
}
/**
* @see org.newdawn.slick.Game#render(org.newdawn.slick.GameContainer,
* org.newdawn.slick.Graphics)
*/
public void render(GameContainer container, Graphics g)
throws SlickException {
// draw the appropriate section of the tilemap based on the centre
// (hence the -(TANK_SIZE/2)) of
// the player
int playerTileX = (int) playerX;
int playerTileY = (int) playerY;
// caculate the offset of the player from the edge of the tile. As the
// player moves around this
// varies and this tells us how far to offset the tile based rendering
// to give the smooth
// motion of scrolling
int playerTileOffsetX = (int) ((playerTileX - playerX) * TILE_SIZE);
int playerTileOffsetY = (int) ((playerTileY - playerY) * TILE_SIZE);
// render the section of the map that should be visible. Notice the -1
// and +3 which renders
// a little extra map around the edge of the screen to cope with tiles
// scrolling on and off
// the screen
map.render(playerTileOffsetX - (PLAYER_SIZE / 2), playerTileOffsetY
- (PLAYER_SIZE / 2), playerTileX - leftOffsetInTiles - 1,
playerTileY - topOffsetInTiles - 1, widthInTiles + 3,
heightInTiles + 3);
// draw entities relative to the player that must appear in the center
// of the screen
g.translate(400 - (int) (playerX * 32), 300 - (int) (playerY * 32));
// draw other entities here if there were any
g.resetTransform();
if (isIntroOver == false) {
int mx = container.getInput().getMouseX();
int my = container.getInput().getMouseY();
g.drawAnimation(circleAnim, mx - 32, my - 32);
g.drawImage(titleImage, x, y);
g.setColor(Color.black);
g.fillRect(0, 450, 800, 150);
g.drawImage(baseBGImage, fx, fy);
g.drawAnimation(brenAnim, rx, ry);
g.drawImage(basePotionImage, px - 50, py + 70);
g.setColor(Color.white);
g.drawRect(0, 450, 799, 149);
}
if (isIntroOver == true){
g.drawImage(baseBGImage, fx, fy);
//g.drawAnimation(brenAnim, rx, ry);
g.drawImage(basePotionImage, px - 50, py + 70);
//g.setColor(Color.black);
//g.fillRect(0, 450, 800, 150);
g.drawAnimation(brenAnim, 300, ry);
g.drawRect(0, 450, 799, 149);
g.drawRect(1, 451, 798, 148);
//long slideTime = System.currentTimeMillis() + 2000;
if (isWizardDrawn == true){
g.translate(400 - (int) (playerX * 32), 300 - (int) (playerY * 32));
if(wizList == null ){
System.out.println("true");
}
}
}
if (fy < 1000 && py < 900 ){
fy = fy + 1;
py = py + 2;
//if (slideCount <=1){
//slideTime = System.currentTimeMillis() + 2000;
//slideCount++;}
//else{
//g.setColor(Color.black);
//g.fillRect(0, 450, 800, 150);}
}
if(container.getInput().isKeyPressed(Input.KEY_ESCAPE)){
isIntroOver = false;
}}
/**
*
*
* @param argv
* The argument passed on the command line (if any)
*/
public static void main(String[] argv) {
try {
// create a new container for our example game. This container
// just creates a normal native window for rendering OpenGL
// accelerated
// elements to
AppGameContainer container = new AppGameContainer(
new MainGameLoop(), 800, 600, false);
container.setAlwaysRender(true);
container.setVSync(true);
container.setShowFPS(false);
container.setMouseGrabbed(false);
container.start();
} catch (Exception e) {
e.printStackTrace();
}
}
}
最佳答案
您的 init 方法初始化一个局部变量:
ArrayList<WizardObject> wizList = new ArrayList <WizardObject>(100);
类成员保持未初始化状态，因此它包含 null(默认值):
public List<WizardObject> wizList;
改变
ArrayList<WizardObject> wizList = new ArrayList <WizardObject>(100);
到
wizList = new ArrayList <WizardObject>(100);
关于Java ArrayList 似乎在 init 方法之后无效，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/29913162/