我在jMonkey Engine 3中制作游戏，我的世界代码有点笨重，所以我打算将它移到一个名为Generator的新类，但是当我终于解决了所有问题并运行了我的程序，我在我试图使用其他类的方法的地方得到NullPointerException。我过去曾经遇到过NullPointerException这么糟糕的运气，但这是最糟糕的一次。代码在主类文件中有效。我将为您提供以下两个类的代码以及错误。
请注意，我不包括包装声明或导入以节省空间。
第一课：主要：
public class Main extends SimpleApplication implements ActionListener {
private static final Logger logger = Logger.getLogger(Main.class.getName());
private BulletAppState bulletAppState;
private CharacterControl playerControl;
private Vector3f walkDirection = new Vector3f();
private boolean[] arrowKeys = new boolean[4];
private CubesSettings cubesSettings;
private BlockTerrainControl blockTerrain;
private Node terrainNode = new Node();
private Generator gen;
public static void main(String[] args){
Logger.getLogger("").setLevel(Level.FINE);
AppSettings s = new AppSettings(true);
Main app = new Main();
try {
s.load("com.bminus");
} catch(BackingStoreException e) {
logger.log(Level.SEVERE, "Could not load configuration settings.",e);
}
try {
s.setIcons(new BufferedImage[]{ImageIO.read(new File("assets/Textures/icon.gif"))});
} catch (IOException e) {
Logger.getLogger(Main.class.getName()).log(Level.SEVERE, "Icon file missing",e);
}
s.setRenderer(AppSettings.LWJGL_OPENGL2);
s.setBitsPerPixel(24);
s.setFrameRate(-1);
s.setFullscreen(false);
s.setResolution(640,480);
s.setSamples(0);
s.setVSync(true);
s.setFrequency(60);
s.setTitle("The Third Power Pre-Alpha 1.1.0");
try {
s.save("com.bminus");
} catch(BackingStoreException e) {
logger.log(Level.SEVERE, "Could not save configuration settings.",e);
}
app.setShowSettings(false);
app.setSettings(s);
app.start();
}
public Main(){}
@Override
public void simpleInitApp(){
setDisplayFps(false);
setDisplayStatView(false);
bulletAppState = new BulletAppState();
stateManager.attach(bulletAppState);
initControls();
gen.initBlockTerrain(); //THIS LINE IS THE ONE THAT IS NULL!!!
initGUI();
initPlayer();
cam.lookAtDirection(new Vector3f(1, 0, 1), Vector3f.UNIT_Y);
}
private void initControls(){
inputManager.addMapping("fps_show", new KeyTrigger(KeyInput.KEY_F3));
inputManager.addMapping("fps_hide", new KeyTrigger(KeyInput.KEY_F4));
inputManager.addMapping("left", new KeyTrigger(KeyInput.KEY_A));
inputManager.addMapping("right", new KeyTrigger(KeyInput.KEY_D));
inputManager.addMapping("forward", new KeyTrigger(KeyInput.KEY_W));
inputManager.addMapping("backward", new KeyTrigger(KeyInput.KEY_S));
inputManager.addMapping("jump", new KeyTrigger(KeyInput.KEY_SPACE));
inputManager.addMapping("place", new MouseButtonTrigger(MouseInput.BUTTON_RIGHT));
inputManager.addMapping("break", new MouseButtonTrigger(MouseInput.BUTTON_LEFT));
inputManager.addListener(this, "fps_show");
inputManager.addListener(this, "fps_hide");
inputManager.addListener(this, "left");
inputManager.addListener(this, "right");
inputManager.addListener(this, "forward");
inputManager.addListener(this, "backward");
inputManager.addListener(this, "jump");
inputManager.addListener(this, "place");
inputManager.addListener(this, "break");
}
private void initGUI(){
BitmapText crosshair = new BitmapText(guiFont);
crosshair.setText("+");
crosshair.setSize(guiFont.getCharSet().getRenderedSize() * 2);
crosshair.setLocalTranslation(
(settings.getWidth() / 2) - (guiFont.getCharSet().getRenderedSize() / 3 * 2),
(settings.getHeight() / 2) + (crosshair.getLineHeight() / 2), 0);
guiNode.attachChild(crosshair);
BitmapText instructionsText1 = new BitmapText(guiFont);
instructionsText1.setText("Left Click: Remove");
instructionsText1.setLocalTranslation(0, settings.getHeight(), 0);
guiNode.attachChild(instructionsText1);
BitmapText instructionsText2 = new BitmapText(guiFont);
instructionsText2.setText("Right Click: Place");
instructionsText2.setLocalTranslation(0, settings.getHeight() - instructionsText2.getLineHeight(), 0);
guiNode.attachChild(instructionsText2);
BitmapText instructionsText3 = new BitmapText(guiFont);
instructionsText3.setText("Bottom Layer Cannot Be Broken");
instructionsText3.setLocalTranslation(0, settings.getHeight() - (2 * instructionsText3.getLineHeight()), 0);
guiNode.attachChild(instructionsText3);
}
private void initPlayer(){
playerControl = new CharacterControl(new CapsuleCollisionShape((cubesSettings.getBlockSize() / 2), cubesSettings.getBlockSize() * 2), 0.05f);
playerControl.setJumpSpeed(25);
playerControl.setFallSpeed(140);
playerControl.setGravity(100);
playerControl.setPhysicsLocation(new Vector3f(5, 257, 5).mult(cubesSettings.getBlockSize()));
bulletAppState.getPhysicsSpace().add(playerControl);
}
@Override
public void simpleUpdate(float lastTimePerFrame) {
float playerMoveSpeed = ((cubesSettings.getBlockSize() * 2.5f) * lastTimePerFrame);
Vector3f camDir = cam.getDirection().mult(playerMoveSpeed);
Vector3f camLeft = cam.getLeft().mult(playerMoveSpeed);
walkDirection.set(0, 0, 0);
if(arrowKeys[0]){ walkDirection.addLocal(camDir); }
if(arrowKeys[1]){ walkDirection.addLocal(camLeft.negate()); }
if(arrowKeys[2]){ walkDirection.addLocal(camDir.negate()); }
if(arrowKeys[3]){ walkDirection.addLocal(camLeft); }
walkDirection.setY(0);
playerControl.setWalkDirection(walkDirection);
cam.setLocation(playerControl.getPhysicsLocation());
}
@Override
public void onAction(String actionName, boolean value, float lastTimePerFrame){
if(actionName.equals("forward")) {
arrowKeys[0] = value;
}
else if(actionName.equals("right")) {
arrowKeys[1] = value;
}
else if(actionName.equals("left")) {
arrowKeys[3] = value;
}
else if(actionName.equals("backward")) {
arrowKeys[2] = value;
}
else if(actionName.equals("jump")) {
playerControl.jump();
}
else if(actionName.equals("fps_show")) {
setDisplayFps(true);
}
else if(actionName.equals("fps_hide")) {
setDisplayFps(false);
}
else if(actionName.equals("place") && value){
Vector3Int blockLocation = getCurrentPointedBlockLocation(true);
if(blockLocation != null){
blockTerrain.setBlock(blockLocation, Block_Wood.class);
}
}
else if(actionName.equals("break") && value){
Vector3Int blockLocation = getCurrentPointedBlockLocation(false);
if((blockLocation != null) && (blockLocation.getY() > 0)){
blockTerrain.removeBlock(blockLocation);
}
}
}
private Vector3Int getCurrentPointedBlockLocation(boolean getNeighborLocation){
CollisionResults results = getRayCastingResults(terrainNode);
if(results.size() > 0){
Vector3f collisionContactPoint = results.getClosestCollision().getContactPoint();
return BlockNavigator.getPointedBlockLocation(blockTerrain, collisionContactPoint, getNeighborLocation);
}
return null;
}
private CollisionResults getRayCastingResults(Node node){
Vector3f origin = cam.getWorldCoordinates(new Vector2f((settings.getWidth() / 2), (settings.getHeight() / 2)), 0.0f);
Vector3f direction = cam.getWorldCoordinates(new Vector2f((settings.getWidth() / 2), (settings.getHeight() / 2)), 0.3f);
direction.subtractLocal(origin).normalizeLocal();
Ray ray = new Ray(origin, direction);
CollisionResults results = new CollisionResults();
node.collideWith(ray, results);
return results;
}
public void attachRootChildTerrain(){ //THIS IS CALLED IN THE GENERATOR CLASS!!
rootNode.attachChild(gen.terrainNode);
}
}
第二类：发电机：
public class Generator {
private CubesSettings cubesSettings;
private BlockTerrainControl blockTerrain;
private final Vector3Int terrainSize = new Vector3Int(1000, 256, 1000);
private final Vector3Int bottomLayer = new Vector3Int(1000,1,1000);
private BulletAppState bulletAppState;
public Node terrainNode = new Node();
private SimpleApplication sa;
private Main main;
public void initBlockTerrain(){
CubesTestAssets.registerBlocks();
CubesTestAssets.initializeEnvironment(sa);
cubesSettings = CubesTestAssets.getSettings(sa);
blockTerrain = new BlockTerrainControl(cubesSettings, new Vector3Int(7, 1, 7));
blockTerrain.setBlocksFromNoise(new Vector3Int(), terrainSize, 20f, Block_Grass.class);
blockTerrain.setBlocksFromNoise(new Vector3Int(), bottomLayer, 0.0f, Block_Stone.class);
blockTerrain.addChunkListener(new BlockChunkListener(){
@Override
public void onSpatialUpdated(BlockChunkControl blockChunk){
Geometry optimizedGeometry = blockChunk.getOptimizedGeometry_Opaque();
RigidBodyControl rigidBodyControl = optimizedGeometry.getControl(RigidBodyControl.class);
if(rigidBodyControl == null){
rigidBodyControl = new RigidBodyControl(0);
optimizedGeometry.addControl(rigidBodyControl);
bulletAppState.getPhysicsSpace().add(rigidBodyControl);
}
rigidBodyControl.setCollisionShape(new MeshCollisionShape(optimizedGeometry.getMesh()));
}
});
terrainNode.addControl(blockTerrain);
terrainNode.setShadowMode(RenderQueue.ShadowMode.CastAndReceive);
main.attachRootChildTerrain();
}
}
错误：
java.lang.NullPointerException
at com.bminus.Main.simpleInitApp(Main.java:110)
at com.jme3.app.SimpleApplication.initialize(SimpleApplication.java:226)
at com.jme3.system.lwjgl.LwjglAbstractDisplay.initInThread(LwjglAbstractDisplay.java:130)
at com.jme3.system.lwjgl.LwjglAbstractDisplay.run(LwjglAbstractDisplay.java:207)
at java.lang.Thread.run(Thread.java:744)
这是我第一次尝试使用多个类。我猜我忘了从Generator类中调用一些东西或者创建一些public而不是private，但我不确定。如果有人能够解决这个问题，我将不胜感激。谢谢！
Exception in thread "main" java.lang.StackOverflowError
at sun.misc.Unsafe.putObject(Native Method)
at java.util.concurrent.ConcurrentLinkedQueue$Node.<init>(ConcurrentLinkedQueue.java:187)
at java.util.concurrent.ConcurrentLinkedQueue.<init>(ConcurrentLinkedQueue.java:255)
at com.jme3.app.Application.<init>(Application.java:94)
at com.jme3.app.SimpleApplication.<init>(SimpleApplication.java:102)
at com.jme3.app.SimpleApplication.<init>(SimpleApplication.java:98)
at com.bminus.Main.<init>(Main.java:88)
at com.bminus.Generator.<init>(Generator.java:31)
at com.bminus.Main.<init>(Main.java:47)
因为它是溢出错误，所以最后两个错误行继续进行！我的代码中被称为错误的行是：
public Main(){}
，
private Main main = new Main();
和
private Generator gen = new Generator(this);
我不确切知道为什么会发生这种情况，但如果你们有人这样做，那么知道如何修复它会很棒。谢谢！
答案 0 :(得分：2)
调试NullPointerException时最重要的是找到抛出异常的行。您尝试在该行上使用的变量为null。
可能的罪魁祸首：
在Main类中，您的Generator变量gen永远不会分配实例，因此为null。通过调用Generator构造函数给它一个实例。
gen = new Generator();
在您的Generator类中，Main字段main为null，因为您从未为其分配Main实例。我建议你给构造函数一个Main参数，这样你就可以将你在main方法中创建的当前使用的Main实例（这些名称令人困惑！）传入你的Generator类，并使用这个参数初始化你的主要字段。
即，
public Generator(Main main) {
//.....
this.main = main; // give the main field an object
}
因此，请更改以上代码以将Generator创建为：
gen = new Generator(this);