Java Slick2D getGraphics（）返回null，出现null指针异常

我正在努力让我的slick2d游戏渲染，但是container.getGraphics（）返回null，我得到一个null指针异常。我使用以下命令检查是否是getGraphics（）返回null：

if (container.getGraphics()==null) return;

这修复了npe，但是我当然不能渲染任何东西

堆栈跟踪：

Tue Sep 02 21:42:19 MDT 2014 INFO:Slick Build #237
Exception in thread "Thread-1" java.lang.NullPointerException
    at com.nonuniversal.client.MenuState.render(MenuState.java:17)
    at org.newdawn.slick.state.StateBasedGame.render(StateBasedGame.java:199)
    at com.nonuniversal.client.Game.run(Game.java:33)
    at java.lang.Thread.run(Unknown Source)

请注意，LunaTopiClient在运行时需要用户名参数

import org.newdawn.slick.AppGameContainer;
import org.newdawn.slick.SlickException;

public class LunatopiaClient{
    private String username;
    AppGameContainer container;
    Game game;

    public LunatopiaClient(String username) {

        this.username = username;

    }
    public static void main(String args[]) {

        if (args.length!=1) {
            System.out.println("Usage: java -jar <filename.jar> <username>");
            return;
        } else {
            LunatopiaClient lunatopiaClient = new LunatopiaClient(args[0]);
            lunatopiaClient.init();
        }

    }
    public void init() {

        try {
            game = new Game("");
            container = new AppGameContainer(game);
            container.setFullscreen(true);
            game.init(container);
            game.init();
        } catch (SlickException e) {
            e.printStackTrace();
        }

    }
    public Game getGame() {
        return game;
    }
    public String getUsername() {
        return username;
    }
}

门努斯特类

import org.newdawn.slick.GameContainer;
import org.newdawn.slick.Graphics;
import org.newdawn.slick.SlickException;
import org.newdawn.slick.state.BasicGameState;
import org.newdawn.slick.state.StateBasedGame;

public class MenuState extends BasicGameState{

    public void init(GameContainer container, StateBasedGame game)
            throws SlickException {

    }
    public void render(GameContainer container, StateBasedGame game, Graphics g)
            throws SlickException {
        g.drawString("Hello World", 0, 0);
    }
    public void update(GameContainer container, StateBasedGame game, int arg)
            throws SlickException {

    }
    public int getID() {
        return 0;
    }

}

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编辑：拼写

不幸的是，您在一个非常非正统的庄园中配置了大量代码。首先，Slick2d将自动执行程序的线程，因此您不需要自己编写线程

您似乎也在调用不存在的方法，例如在游戏中未定义init（容器）。此外，您将容器存储为不需要的数据值，因此您将获得图形上下文的NPE

---

如果你刚刚开始使用Slick2d，我建议你看看Newboston关于如何开始的视频教程。否则，我相信您可能必须重新启动您的项目，因为它在当前状态下不可用。希望这能有所帮助：）

嘿，谢谢你的回答，我终于弄明白了，而且进展顺利！

import org.newdawn.slick.GameContainer;
import org.newdawn.slick.Graphics;
import org.newdawn.slick.SlickException;
import org.newdawn.slick.state.BasicGameState;
import org.newdawn.slick.state.StateBasedGame;

public class MenuState extends BasicGameState{

    public void init(GameContainer container, StateBasedGame game)
            throws SlickException {

    }
    public void render(GameContainer container, StateBasedGame game, Graphics g)
            throws SlickException {
        g.drawString("Hello World", 0, 0);
    }
    public void update(GameContainer container, StateBasedGame game, int arg)
            throws SlickException {

    }
    public int getID() {
        return 0;
    }

}