Reflection调用NullPointerException

Question

好的，在过去的几天里，我一直在努力学习如何在Java中使用反射。

到目前为止，我做得还不错，但是当我尝试在类的实例上调用方法时，我会陷入停顿状态。

    } else if(commandName.equals("speak")) {
        try {
            Object stream = getField("stream").get(client);
            Object aStream = getField("aStream_834").get(client);

            Class<? extends Object> streamC = stream.getClass();
            Class<? extends Object> aStreamC = aStream.getClass();
            Class<? extends Object> textInputClass = textInput.getClass();

            Method createFrame = streamC.getDeclaredMethod("createFrame", int.class);

            createFrame.invoke(stream, 4); // this is line 32
            streamC.getDeclaredMethod("writeWordBigEndian", int.class).invoke(stream, 0);
            int offset = stream.getClass().getDeclaredField("currentOffset").getInt(stream);
            streamC.getDeclaredMethod("method425", int.class).invoke(stream, 0);
            streamC.getDeclaredMethod("method425", int.class).invoke(stream, 0);
            aStreamC.getField("currentOffset").set(client,  0);
            textInputClass.getDeclaredMethod("method526", String.class, aStreamC).invoke(textInput, "Hello", aStream);
            int buf = aStreamC.getField("buffer").getInt(aStream);
            streamC.getDeclaredMethod("method441", int.class, byte.class, int.class).invoke(stream, 0, buf, offset);
            streamC.getDeclaredMethod("writeBytes", int.class).invoke(stream, (stream.getClass().getField("currentOffset").getInt(stream) - offset));
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (SecurityException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            //e.printStackTrace();
            e.getCause().printStackTrace();
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        }
    }

我的错误如下：

java.lang.NullPointerException
at vscapeClient.Stream.createFrame(Stream.java:46)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at in.programm.bot.Bot.handleCommand(Bot.java:32)
at in.programm.bot.Gui$1.actionPerformed(Gui.java:35)

“客户”来自这里：

public static Object client = null;
public static Object textInput = null;
public static String pkg = "vscapeClient/";

public static void main(String args[]) {
    try {
        Gui.main(null);
        URL[] urls = { new URL("jar:file:vscape.jar!/") };
        URLClassLoader classLoader = URLClassLoader.newInstance(urls);
        Class<?> c = classLoader.loadClass(pkg.replaceAll("/", ".") + "client");
        textInput = classLoader.loadClass(pkg.replaceAll("/", ".") + "TextInput");
        String[] strings = {""};
        client = c.newInstance();
        client.getClass().getDeclaredMethod("main", strings.getClass()).invoke(client, (Object) strings);
        Field[] fields = client.getClass().getDeclaredFields();
        Method[] methods = client.getClass().getDeclaredMethods();
        for(Field f : fields) {
            f.setAccessible(true);
        }
        for(Method m : methods) {
            m.setAccessible(true);
        }
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e1) {
        e1.printStackTrace();
    } catch (NoSuchMethodException e1) {
        e1.printStackTrace();
    } catch (SecurityException e1) {
        e1.printStackTrace();
    } catch (IllegalArgumentException e1) {
        e1.printStackTrace();
    } catch (InvocationTargetException e1) {
        e1.printStackTrace();
    } catch (InstantiationException e) {
        e.printStackTrace();
    }
}

这可能不重要，但这是Stream.java的第46行（this.buffer [（this .......）

public byte[] buffer;
public int currentOffset;
public ISAACRandomGen encryption;

public void createFrame(int i)
{
  this.buffer[(this.currentOffset++)] = ((byte)(i + this.encryption.getNextKey()));
}