super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

if (Build.VERSION.SDK_INT >= 21) {

  View decorView = getWindow().getDecorView();

  int option = View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN

      | View.SYSTEM_UI_FLAG_LAYOUT_STABLE;

  decorView.setSystemUiVisibility(option);

  getWindow().setStatusBarColor(Color.TRANSPARENT);

}

ActionBar actionBar = getSupportActionBar();

actionBar.hide();

原文链接：https://blog.csdn.net/guolin_blog/article/details/51763825