Question

我正在制作游戏，但我遇到了这个恼人的问题。试图google它但到目前为止没有运气。我在自己的文件中定义了一个类（这里的代码不是我的游戏，而是一个有相同错误的简化版）：

package graf.grafika;

public class MyClass {
    int number;
}

问题出在myMethod（应用程序意外停止）：

public class aktivnost extends Activity {
    MyClass[] myclass = new MyClass[5];

    void myMethod()
    {
        //Error
        myclass[0].number = 1;
    }

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        myMethod();
        setContentView(new Panel(this));
    }
...other required methods
}

logcat的：

07-02 10:01:13.507: ERROR/AndroidRuntime(3203): FATAL EXCEPTION: main
07-02 10:01:13.507: ERROR/AndroidRuntime(3203): java.lang.RuntimeException: Unable to start activity ComponentInfo{graf.grafika/graf.grafika.aktivnost}: java.lang.NullPointerException
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1736)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1752)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at android.app.ActivityThread.access$1500(ActivityThread.java:123)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:993)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at android.os.Handler.dispatchMessage(Handler.java:99)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at android.os.Looper.loop(Looper.java:126)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at android.app.ActivityThread.main(ActivityThread.java:3997)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at java.lang.reflect.Method.invokeNative(Native Method)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at java.lang.reflect.Method.invoke(Method.java:491)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at dalvik.system.NativeStart.main(Native Method)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203): Caused by: java.lang.NullPointerException
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at graf.grafika.aktivnost.myMethod(aktivnost.java:17)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at graf.grafika.aktivnost.onCreate(aktivnost.java:23)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1048)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1700)
07-02 10:01:13.507: ERROR/AndroidRuntime(3203):     ... 11 more

有人可以帮我解决这个问题吗？我不熟悉java编程。

Answer 1

在数组中实际放入5个新类：

MyClass[] myclass = new MyClass[5];
for(int i = 0; i < 5; i++)
{
myclass[i] = new MyClass();
}

Answer 2

myclass[0]为null，因为它不指向任何对象。这就是你得到空指针的原因。你应该myclass[0] = new MyClass();

public class aktivnost extends Activity {
    MyClass[] myclass = new MyClass[5];

    void myMethod()
    {
        //Error
        myclass[0] = new MyClass(); 
        myclass[0].number = 1;
    }

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        myMethod();
        setContentView(new Panel(this));
    }
...other required methods
}

Answer 3

MyClass [] myclass = new MyClass [5]; 表示初始化数组对象，而不是单个对象，您应该初始化您希望在数组对象中使用它们的单个对象，如myclass [0] = new MyClass（）;

需要有关Android NullPointer问题的帮助

3 个答案: