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POWhy does this cause a NullPointerException?
 

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  1. POWhy does this cause a NullPointerException?
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    <p>I have a program which is as follows, Can anyone tell me what is the reason for getting an NPE.</p> <pre><code>public class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); secondClass x = new secondClass(); x.sText("Test Spring"); } } public class secondClass extends MainActivity { public void sText(String s) { TextView text = (TextView) findViewById(R.id.text); text.setText(s); } } </code></pre> <p><strong>Mainfest</strong></p> <pre><code>&lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" ... &lt;TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/hello_world" android:id="@+id/text" /&gt; &lt;/RelativeLayout&gt; </code></pre> <p><strong>LogCat</strong></p> <pre><code>08-16 01:31:11.320 15032-15032/? E/Trace: error opening trace file: No such file or directory (2) 08-16 01:31:11.420 836-987/? E/EmbeddedLogger: App crashed! Process: com.example.myapplication 08-16 01:31:11.420 836-987/? E/EmbeddedLogger: App crashed! Package: com.example.myapplication v1 (1.0) 08-16 01:31:11.420 836-987/? E/EmbeddedLogger: Application Label: My Application 08-16 01:31:11.420 15032-15032/? E/AndroidRuntime: FATAL EXCEPTION: main java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapplication/com.example.myapplication.MainActivity}: java.lang.NullPointerException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java) at android.app.ActivityThread.access$600(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java) at android.os.Handler.dispatchMessage(Handler.java) at android.os.Looper.loop(Looper.java) at android.app.ActivityThread.main(ActivityThread.java) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java) at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:110) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException at android.app.Activity.findViewById(Activity.java) at com.example.myapplication.secondClass.sText(secondClass.java:13) at com.example.myapplication.MainActivity.onCreate(MainActivity.java:14) at android.app.Activity.performCreate(Activity.java) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java) </code></pre> <p>To my understanding, this should instantiate and initialize a secondClass object then call its sText() method. The sText method should then store a reference in TextView. Next it calls the setText() method on TextView, which changes the text in the TextView to what was passed into sText().</p> <p>The logcat says it throws a NullPointerException but I'm not entirely sure why. If this is a rookie mistake, it's because I am a rookie. Thank you.</p>
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    1. USTevin J
    1. USTevin J
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      1. POWhy does this cause a NullPointerException?
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    2. VO
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      1. POWhy does this cause a NullPointerException?
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    1. COWhy do you need `secondClass`?
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      1. POWhy does this cause a NullPointerException?
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    2. COCould you post your logcat, might help
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      1. POWhy does this cause a NullPointerException?
      1. USDavid Liaw
    3. COCan you share more details what are you trying to archive. Having two activities instances is super rare case as well accessing one from another is not the way how android works
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      1. POWhy does this cause a NullPointerException?
      1. USEugen Martynov
 

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