java - 编码中线程 "main"java.lang.NullPointerException 异常

Question

我很确定这些问题已经被问了数百万次，但不幸的是，我找不到答案。

Exception in thread "main" java.lang.NullPointerException
    at com.bluebitgames.visualnovel.Game.initStatesList(Game.java:30)
    at org.newdawn.slick.state.StateBasedGame.init(StateBasedGame.java:164)
    at org.newdawn.slick.AppGameContainer.setup(AppGameContainer.java:390)
    at org.newdawn.slick.AppGameContainer.start(AppGameContainer.java:314)
    at com.bluebitgames.visualnovel.Game.main(Game.java:77)

我知道 java.lang.NullPointerException 意味着该变量具有空值，因此我必须更改它，但我真的不知道。

package com.bluebitgames.visualnovel;

import org.newdawn.slick.AppGameContainer;
import org.newdawn.slick.GameContainer;
import org.newdawn.slick.SlickException;
import org.newdawn.slick.UnicodeFont;
import org.newdawn.slick.font.effects.ColorEffect;
import org.newdawn.slick.state.StateBasedGame;

public class Game extends StateBasedGame {
        public static final int SCREEN_WIDTH        = 1024;
        public static final int SCREEN_HEIGHT        = 640;
        public static final String title        = "Visual Novel";
        public static final String version        = "";
        public static final String vDate        = "03/07/12";

        // States
        public static final int menu  = 0;
        public static final int play  = 1;

        // Main font
        public static UnicodeFont font;

        public Game(String title) {
                super(title);
                this.addState(new Play(play));
        }

        public void initStatesList(GameContainer gc) throws SlickException {
                this.getState(menu).init(gc, this);     //line 30
                this.getState(play).init(gc, this);
                this.enterState(menu);
        }



        @SuppressWarnings("unchecked")
        public static UnicodeFont mainFont(int size, String name) {
                if(name.equals("default")) {
                        name        = "tempesta";
                }
                UnicodeFont font;
                try {
                        font        = new UnicodeFont("res/fonts/"+name+".ttf", size, false, false);
                        font.addAsciiGlyphs();
                        font.addGlyphs(400, 600);
                        font.getEffects().add(new ColorEffect(java.awt.Color.WHITE));
                        font.loadGlyphs();
                        return font;
                } catch(SlickException e) {
                        System.out.println("Could not load font.");
                        e.printStackTrace();
                        return null;
                }

        }

        public static void main(String[] args) {
                String os        = System.getProperty("os.name");
                if(os.contains("Windows")) {
                        os        = "windows";
                } else if(os.contains("Mac")) {
                        os        = "macosx";
                } else {
                        os        = "linux";
                }

                System.setProperty("org.lwjgl.librarypath",System.getProperty("user.dir") + "/lib/natives/"+os);
                AppGameContainer agc;
                try {
                        agc        = new AppGameContainer(new Game(title+" v"+version));
                        agc.setDisplayMode(SCREEN_WIDTH, SCREEN_HEIGHT, false);
                        //agc.setFullscreen(true);
                        agc.setTargetFrameRate(60);
                        agc.setShowFPS(true);
                        agc.setVSync(true);
                        agc.start();      //line 77
                } catch(SlickException e) {
                        e.printStackTrace();
                }
        }
}

(StateBasedGame 和 AppGameContainer 是名为“Slick”的 .jar 的类，我不知道如何为其提供编码。抱歉!)

希望有人能帮我解决这个问题。

编辑:对此感到非常抱歉。刚刚编辑过。

Answer 1

我不知道Slick2D，但您似乎在构造函数中添加了播放状态而不是菜单状态，并且当您尝试调用菜单状态上的方法时似乎会抛出NPE。我很高兴，但也许你也应该在构造函数中初始化菜单状态。

如果答案有误，请原谅并删除答案。