how to show send a warning in android code example

Example: android alert builder code

AlertDialog alertDialog = new AlertDialog.Builder(getApplicationContext())
    .setIcon(android.R.drawable.ic_dialog_alert)
	.setTitle("Goodbye!")
    .setMessage("Are you sure you want to exit?")
    .setPositiveButton("Yes", new DialogInterface.OnClickListener()
    {
       @Override
       public void onClick(DialogInterface dialogInterface, int i)
       {
          finish();
       }
    })
	
    .setNegativeButton("No", new DialogInterface.OnClickListener()
    {
        @Override
        public void onClick(DialogInterface dialogInterface, int i)
        {
          Toast.makeText(getApplicationContext(),"Nothing Happened",Toast.LENGTH_LONG).show();
        }
    }).show();