‘getHeaders()’ : It return a map of the request headers.where the key string contains the name of the header, and the value string contains the value of the header.
After that get the ‘Host’ key value from that map

‘getUrl()’ : It returns the relative URL associated with the PageReference when it was originally defined, including any query string parameters and anchors.

Apex Code :

public with sharing class pageurlclass{
    public  String  headerdata{get;set;}
    public string urlvalue{get;set;}
    public string url{get;set;}
        
    public pageurlclass(){
        
         headerdata= ApexPages.currentPage().getHeaders().get('Host');
        
         urlvalue=Apexpages.currentPage().getUrl();
        
         url='https://' + headerdata+ urlvalue;
    }
  

}

 

Visualforce Page : Create visualforce page with name Pageurl

<apex:page controller="pageurlclass">
      
  1.  {!headerdata}

  2.  {!urlvalue}

  3.  {!url}

</apex:page>

Output

1. c.ap2.visual.force.com

2. /apex/Pageurl

3. https://c.ap2.visual.force.com/apex/Pageurl

Read More: Test Classes In Apex Salesforce