使用Libgdx Book开发Java游戏第3章ClassNotFoundException

Question

我看到别人问这个问题，但那是两年多前的事了，他们一直没有得到答案。我试图用LibGDX运行Java Game Development一书中的一个示例程序，但我遇到了一个奇怪的错误。错误如下：

java.lang.ClassNotFoundException: Rock
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:606)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:168)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
at java.base/java.lang.Class.forName0(Native Method)
at java.base/java.lang.Class.forName(Class.java:377)
at com.mygdx.game.BaseActor.getList(BaseActor.java:319)
at com.mygdx.game.StarfishCollector.update(StarfishCollector.java:35)
at com.mygdx.game.GameBeta.render(GameBeta.java:24)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:232)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:127)
Exception in thread "LWJGL Application" java.lang.NullPointerException: Cannot invoke "java.lang.Class.isInstance(Object)" because "theClass" is null
at com.mygdx.game.BaseActor.getList(BaseActor.java:326)
at com.mygdx.game.StarfishCollector.update(StarfishCollector.java:35)
at com.mygdx.game.GameBeta.render(GameBeta.java:24)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:232)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:127)
11:45:50 PM: Task execution finished 'DesktopLauncher.main()'.

我正在使用intelliJ，源代码可以找到：https://github.com/Apress/java-game-dev-LibGDX/blob/master/Ch03%20Starfish%20Collector/BaseActor.java而且https://github.com/Apress/java-game-dev-LibGDX/blob/master/Ch03%20Starfish%20Collector/StarfishCollector.java

该方法的代码为：

public static ArrayList<BaseActor> getList(Stage stage, String className)
{
ArrayList<BaseActor> list = new ArrayList<BaseActor>();

Class theClass = null;
try
{  theClass = Class.forName(className);  }
catch (Exception error)
{  error.printStackTrace();  }

for (Actor a : stage.getActors())
{
if ( theClass.isInstance( a ) )
list.add( (BaseActor)a );
}
return list;
}

和

new Starfish(400,400, mainStage);
new Starfish(500,100, mainStage);
new Starfish(100,450, mainStage);
new Starfish(200,250, mainStage);

new Rock(200,150, mainStage);
new Rock(100,300, mainStage);
new Rock(300,350, mainStage);
new Rock(450,200, mainStage);

turtle = new Turtle(20,20, mainStage);

win = false;
}
public void update(float dt)
{
for (BaseActor rockActor : BaseActor.getList(mainStage, "Rock"))
turtle.preventOverlap(rockActor);
for (BaseActor starfishActor : BaseActor.getList(mainStage, "Starfish"))
{
Starfish starfish = (Starfish)starfishActor;
if ( turtle.overlaps(starfish) && !starfish.collected )
{
starfish.collected = true;
starfish.clearActions();
starfish.addAction( Actions.fadeOut(1) );
starfish.addAction( Actions.after( Actions.removeActor() ) );
Whirlpool whirl = new Whirlpool(0,0, mainStage);
whirl.centerAtActor( starfish );
whirl.setOpacity(0.25f);
}
}

它似乎找不到类名rock，所以class变量保持为null并导致错误。我希望有人能找到解决方案，因为除此之外，这是一本很棒的书。

感谢

Answer 1

这对我来说很有效，你必须包括包，而不仅仅是类名

theClass = Class.forName("com.mygdx.game." + className);