Question

intentTest.java:

    package intentTest.xyz.com;

     import android.app.Activity;
   import android.content.Intent;
   import android.os.Bundle;
  import android.view.View;
  import android.widget.Button;

      public class intentTest extends Activity {
      Button b;
            /** Called when the activity is first created. */
     @Override
      public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
         b = (Button) findViewById(R.id.b);

        b.setOnClickListener( new View.OnClickListener() {
           public void onClick(View view) {
            Intent intent = new Intent(intentTest.this,seond.class );
            startActivity(intent);

           }

       });

    }
}

main.xml:

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:orientation="vertical"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
  >
   <TextView  
       android:layout_width="fill_parent" 
      android:layout_height="wrap_content" 
       android:text="First screen"
      />

   <Button
      android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="click"
     android:name="@+id/b"
     />
    </LinearLayout>

seond.java:

package intentTest.xyz.com;

import android.app.Activity;
import android.os.Bundle;

public class seond extends Activity{
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.second);

     }
 }

second.xml:

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content">


    <TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
   android:text="second screen"
     />

manifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
  package="intentTest.xyz.com"
  android:versionCode="1"
  android:versionName="1.0">
<application android:icon="@drawable/icon" android:label="@string/app_name">
    <activity android:name=".intentTest"
              android:label="@string/app_name">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

<activity android:name=".seond"></activity>
</application>


</manifest> 

i get the following error code:

11-16 01:26:07.156: ERROR/AndroidRuntime(779): Uncaught handler: thread main exiting  due to uncaught exception
11-16 01:26:07.166: ERROR/AndroidRuntime(779): java.lang.RuntimeException: Unable to start activity ComponentInfo{intentTest.xyz.com/intentTest.xyz.com.intentTest}: java.lang.NullPointerException
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2401)
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2417)
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     at android.app.ActivityThread.access$2100(ActivityThread.java:116)
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     at android.os.Handler.dispatchMessage(Handler.java:99)
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     at android.os.Looper.loop(Looper.java:123)
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     at android.app.ActivityThread.main(ActivityThread.java:4203)
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     at java.lang.reflect.Method.invokeNative(Native Method)
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     at java.lang.reflect.Method.invoke(Method.java:521)
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:549)
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     at dalvik.system.NativeStart.main(Native Method)
11-16 01:26:07.166: ERROR/AndroidRuntime(779): Caused by: java.lang.NullPointerException
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     at intentTest.xyz.com.intentTest.onCreate(intentTest.java:18)
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123)
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364)
11-16 01:26:07.166: ERROR/AndroidRuntime(779):     ... 11 more

Answer 1

Look at the main.xml file, you have made a little mistake that leads to a lot of discussion sometimes.

android:name="@+id/b"

it should be like:

android:id="@+id/b"

So that you can access this element in your activity and that’s why your application causing

NullPointerException 

By the way you are using small letters in class name and capital letters in package name which is not a good practice for coders.