Window w = this.getWindow();
   WindowManager.LayoutParams attributes = w.getAttributes();
  if (attributes.layoutInDisplayCutoutMode != WindowManager.LayoutParams.LAYOUT_IN_DISPLAY_CUTOUT_MODE_SHORT_EDGES) {
   attributes.layoutInDisplayCutoutMode = WindowManager.LayoutParams.LAYOUT_IN_DISPLAY_CUTOUT_MODE_SHORT_EDGES;
  }
  if ((w.getDecorView().getSystemUiVisibility() & View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN) == 0) {
   w.getDecorView().setSystemUiVisibility(View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN);
  }

final Toast toast = new Toast(getApplicationContext()); toast.setDuration(Toast.LENGTH_LONG);
toast.setView(R.layout.TypeYourLayout); 
toast.show();


TypeYourLayout = Create and add your custom view

#code by ninja coder

AlertDialog alertDialog = new AlertDialog.Builder(this,
    android.R.style.Theme_DeviceDefault_Light_NoActionBar_Fullscreen).create();
  alertDialog.setTitle("this Full Screen AlertDialog");
  alertDialog.setMessage("This is Full Screen");
  alertDialog.setButton(AlertDialog.BUTTON_NEUTRAL, "OK", new DialogInterface.OnClickListener() {
   @Override
   public void onClick(DialogInterface dialog, int which) {
    dialog.dismiss();
   }
  });
  alertDialog.show();