Java NullPointerException Collision 是来源，但不确定为什么

Question

我尝试过运行代码而不会发生冲突，并且运行良好。但有了它，我得到了 NullPointerException。问题的根源与编辑有关

blocked[xAxis][yAxis] = true;

：抱歉没有提前提供痕迹。

控制台：

Wed Dec 21 20:32:52 PST 2011 INFO:Slick Build #274
Wed Dec 21 20:32:52 PST 2011 INFO:LWJGL Version: 2.8.2
Wed Dec 21 20:32:52 PST 2011 INFO:OriginalDisplayMode: 1440 x 900 x 32 @60Hz
Wed Dec 21 20:32:52 PST 2011 INFO:TargetDisplayMode: 800 x 600 x 0 @0Hz
Wed Dec 21 20:32:53 PST 2011 INFO:Starting display 800x600
Wed Dec 21 20:32:53 PST 2011 INFO:Use Java PNG Loader = true
Loading: net.java.games.input.DirectAndRawInputEnvironmentPlugin
Wed Dec 21 20:32:54 PST 2011 INFO:Found 0 controllers
Exception in thread "main" java.lang.NullPointerException
at RPG.Main.init(Main.java:41)
at org.newdawn.slick.AppGameContainer.setup(AppGameContainer.java:390)
at org.newdawn.slick.AppGameContainer.start(AppGameContainer.java:314)
at RPG.Main.main(Main.java:102)

TiledMap 属性

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE map SYSTEM "http://mapeditor.org/dtd/1.0/map.dtd">
<map version="1.0" orientation="orthogonal" width="10" height="10" tilewidth="32"                   <tileheight="32">
<tileset name="wall" firstgid="1" tilewidth="32" tileheight="32">
<image source="wall.png"/>
<tile id="0">
<properties>
<property name="blocked" value="true"/>
</properties>
</tile>
</tileset>
<tileset name="grass" firstgid="2" tilewidth="32" tileheight="32">
<image source="grass.png"/>
</tileset>
<layer name="Layer 0" width="10" height="10">
<data encoding="base64" compression="gzip">
H4sIAAAAAAAAAGNkYGBgJBIzEcCUqBvsYtTwLzEYAHHwHBmQAQAA
</data>
</layer>
</map>

完整代码。

public class Main extends BasicGame {

Image player = null;
Image land = null;

private float playerX = 32f;
private float playerY = 32f;
private static final int SIZE = 32;

private boolean[][] blocked;

private TiledMap map;


public Main()
{
    super("Classic");
}

@Override
public void init(GameContainer gc)
        throws SlickException 
{
    player = new Image("RPG/player.png");
    map = new TiledMap("RPG/Map.tmx");

    for (int xAxis=0;xAxis<map.getWidth(); xAxis++)
    {
         for (int yAxis=0;yAxis<map.getHeight(); yAxis++)
         {
             int tileID = map.getTileId(xAxis, yAxis, 0);
             String value = map.getTileProperty(tileID, "blocked", "false");
             if ("true".equals(value))
             {
                 blocked[xAxis][yAxis] = true;
             }
         }
     }

}

@Override
public void update(GameContainer gc, int delta)
        throws SlickException
{
    Input input = gc.getInput();

    if (input.isKeyDown(Input.KEY_LEFT)) {
        if (!isBlocked(playerX, playerY - delta * 0.1f))
        {
        playerX-= delta * 0.1f;
        }
    }
    if (input.isKeyDown(Input.KEY_RIGHT)) {
        if (!isBlocked(playerX, playerY - delta * 0.1f))
        {
        playerX+= delta * 0.1f;
        }
    }
    if (input.isKeyDown(Input.KEY_UP)) {
        if (!isBlocked(playerX, playerY - delta * 0.1f))
        {
        playerY-= delta * 0.1f;
        }
    }
    if (input.isKeyDown(Input.KEY_DOWN)) {
        if (!isBlocked(playerX, playerY - delta * 0.1f))
        {
        playerY+= delta * 0.1f;
        }
    }

}

public void render(GameContainer gc, Graphics g)
        throws SlickException
{
    map.render(0, 0);

    player.draw(playerX, playerY);

}

private boolean isBlocked(float playerX, float playerY)
{
    int xBlock = (int)playerX / SIZE;
    int yBlock = (int)playerY / SIZE;
    return blocked[xBlock][yBlock];
}

public static void main(String[] args)
        throws SlickException
{
     AppGameContainer app = new AppGameContainer( new Main() );
     app.setDisplayMode(800, 600, false);
     app.start();
   }

}

Answer 1

blocked 永远不会被创建。你需要在某个地方说：

blocked = new boolean[xsize][ysize];

xsize 和 ysize 被适当设置。

因为您还没有这样做，所以 blocked 是 null 而不是数组。这就是为什么当您尝试将某些内容分配给数组中的元素时会出现异常的原因。

对于您的情况，您可以添加

blocked = new boolean[map.getWidth()][map.getHeight()];

到 init() 函数的顶部。

Answer 2

您没有初始化数组

private boolean[][] blocked;

，这就是为什么您在 blocked[xAxis][yAxis] = true; 中收到 NullPointerException 的原因

Answer 3

我没有看到在任何地方初始化的阻塞二维数组，您需要将其初始化为地图的大小