title: NullPointerException when creating OnClickListener (Android)
body: <p>This is a very simple android app. I'm just learning to write code for android now and I am unsure why the line: add.setOnClickListener(new View.OnClickListener() throws a NullPointerException. </p>
  
  <pre><code>public class StartingPoint extends ActionBarActivity{
  
  int counter;
  Button add, sub;
  TextView display;
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_starting_point);
  
      if (savedInstanceState == null) {
          getSupportFragmentManager().beginTransaction()
      .add(R.id.container,  new PlaceholderFragment()).commit();
      }
  
      counter = 0;
      add = (Button) findViewById(R.id.bAdd);
      sub = (Button) findViewById(R.id.bSub);
      display = (TextView) findViewById(R.id.tvDisplay);
  
      add.setOnClickListener(new View.OnClickListener() 
      {
  
          @Override
          public void onClick(View v) 
          {
              counter++;
              display.setText("Your total is " + counter);
          }
      });
  
      sub.setOnClickListener(new View.OnClickListener() 
      {
  
          @Override
          public void onClick(View v) 
          {
              counter--;  
              display.setText("Your total is " + counter);
          }
      });
  
  }
  </code></pre>
  
  <p>Here is the XML code:</p>
  
  <pre><code>&lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:paddingBottom="@dimen/activity_vertical_margin"
  android:paddingLeft="@dimen/activity_horizontal_margin"
  android:paddingRight="@dimen/activity_horizontal_margin"
  android:paddingTop="@dimen/activity_vertical_margin"
  tools:context="com.thenewboston.jaredh.StartingPoint$PlaceholderFragment" &gt;
  
  &lt;TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerHorizontal="true"
      android:text="@string/total"
      android:textSize="40sp" 
      android:id="@+id/tvDisplay"
      /&gt;
  
  &lt;Button
      android:layout_width="250dp"
      android:layout_height="wrap_content"
      android:layout_alignLeft="@+id/tvDisplay"
      android:layout_below="@+id/tvDisplay"
      android:layout_gravity="center"
      android:text="@string/addButton"
      android:textSize="20sp"
      android:id="@+id/bAdd" /&gt;
  
  &lt;Button
      android:layout_width="250dp"
      android:layout_height="wrap_content"
      android:layout_alignLeft="@+id/bAdd"
      android:layout_below="@+id/bAdd"
      android:layout_gravity="center"
      android:text="@string/subButton"
      android:textSize="20sp" 
      android:id="@+id/bSub"/&gt;
  </code></pre>
  
  <p></p>
  
  <pre><code>Logcat Error:
         03-29 17:44:24.930: D/AndroidRuntime(25367): Shutting down VM
  03-29 17:44:24.930: W/dalvikvm(25367): threadid=1: thread exiting with uncaught exception (group=0x41831898)
  03-29 17:44:24.940: E/AndroidRuntime(25367): FATAL EXCEPTION: main
  03-29 17:44:24.940: E/AndroidRuntime(25367): java.lang.RuntimeException: Unable to start activity ComponentInf{com.thenewboston.jaredh/com.thenewboston.jaredh.StartingPoint}: java.lang.NullPointerException
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2305)
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2359)
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at android.app.ActivityThread.access$700(ActivityThread.java:165)
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1326)
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at android.os.Handler.dispatchMessage(Handler.java:99)
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at android.os.Looper.loop(Looper.java:137)
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at android.app.ActivityThread.main(ActivityThread.java:5455)
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at java.lang.reflect.Method.invokeNative(Native Method)
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at java.lang.reflect.Method.invoke(Method.java:525)
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1187)
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at dalvik.system.NativeStart.main(Native Method)
  03-29 17:44:24.940: E/AndroidRuntime(25367): Caused by: java.lang.NullPointerException
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at com.thenewboston.jaredh.StartingPoint.onCreate(StartingPoint.java:39)
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at android.app.Activity.performCreate(Activity.java:5372)
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104)
  03-29 17:44:24.940: E/AndroidRuntime(25367):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2267)
  03-29 17:44:24.940: E/AndroidRuntime(25367):    ... 11 more
  </code></pre>
  
  <p>As you can see it is a very simple app just adding 1 to the text field when either button is clicked. Any help could be greatly apprecitated. Just unsure why the NullPointerException is being caused.</p>