title: Unfortunately app has stopped in emulator and on my phone
body: <p>I just started programming android. As the title says my app stops after i launch it. It would be nice if u could help me.
  If u need any other code or something, just tell me i will post it as soon as i can.</p>
  
  <pre><code>public class MainActivity extends ActionBarActivity {
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
         final MediaPlayer mp;
         Button one; 
  
          mp = MediaPlayer.create(this, R.raw.button);
          one = (Button)this.findViewById(R.id.button1);
  
          one.setOnClickListener(new View.OnClickListener() {
  
             @Override
             public void onClick(View v) {
                 // TODO Auto-generated method stub
  
                 mp.start();
             }
         });
  
  
      if (savedInstanceState == null) {
          getSupportFragmentManager().beginTransaction()
                  .add(R.id.container, new PlaceholderFragment()).commit();
      }
  }
  
  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
  
      // Inflate the menu; this adds items to the action bar if it is present.
      getMenuInflater().inflate(R.menu.main, menu);
      return true;
  }
  
  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
      // Handle action bar item clicks here. The action bar will
      // automatically handle clicks on the Home/Up button, so long
      // as you specify a parent activity in AndroidManifest.xml.
      int id = item.getItemId();
      if (id == R.id.action_settings) {
          return true;
      }
      return super.onOptionsItemSelected(item);
  }
  
  /**
   * A placeholder fragment containing a simple view.
   */
  public static class PlaceholderFragment extends Fragment {
  
      public PlaceholderFragment() {
      }
  
      @Override
      public View onCreateView(LayoutInflater inflater, ViewGroup container,
              Bundle savedInstanceState) {
          View rootView = inflater.inflate(R.layout.fragment_main, container,
                  false);
          return rootView;
      }
  }
  
  }
  </code></pre>