getApplicationContext()空指针

public class InsertActivity extends Activity {
private String TAG = "InsertAPK";
// private Context context = getApplicationContext();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_insert);
initService.startMyServices(getApplicationContext());
Log.d(TAG, "服务启动： "+initService.isServiceRunning());
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.insert, menu);
return true;
}

}

今天在写代码的时候发现一直有错误，后来才发现注释的那行（第三行）的问题，这句话会导致空指针错误，但是为什么呢？不得而知