In onCreate function:

Between ;

 super.onCreate(savedInstanceState);

and 

 setContentView(R.layout.activity_main);


add these codes:

 //Remove title bar
 this.requestWindowFeature(Window.FEATURE_NO_TITLE);

 //Remove notification bar
 this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
 WindowManager.LayoutParams.FLAG_FULLSCREEN);


Reference: http://stackoverflow.com/questions/2591036/how-to-hide-the-title-bar-for-an-activity-in-xml-with-existing-custom-theme

Worked for me ;)