You are calling getResources() before the super.onCreate(Bundle) is called. You must call getResources() after onCreate(). Move your code to onCreate or onStart:
java
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
DisplayMetrics display = getResources().getDisplayMetrics();
int width = display.widthPixels;
int height = display.heightPixels;
}