如何全屏啊 友善的大哥大姐们教教我啊

public class Hellotest extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        this.requestWindowFeature(Window.FEATURE_NO_TITLE);//去掉标题栏

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

        setContentView(R.layout.activity_hellotest);
    }



}