how a page is password protected in wordpress code example

Example 1: password protected website wordpress

In Wordpress by default there is a option for adding password to the page, just
change the "status & visibility" option from public to password protected

Example 2: wordpress check if page is password protected

//post id is optional
if(post_password_required($post_id)) {}
//or
if(!empty($post->post_password)){
   // do some stuff
}