I need an explanation for this program.class Directory{ Node head,tail; Directory() { head=null; tail=null; } public void insert(Node node) // method that insers node into list if phone number is new { Node temp=head; while(temp!=null && !temp.phone_number.equals(node.phone_number)) temp=temp.next; if(temp!=null) { System.out.println("Entered phone number already exists"); return; } if(head==null) { head=node; tail=node; } else { tail.next=node; tail=node; } System.out.println("Inserted Successfully"); } public void remove(String ph_no) // method that removes node with given phone number { Node prev=null; Node node=head; while(node!=null && !node.phone_number.equals(ph_no)) { prev=node; node=node.next; } if(node==null) System.out.println("Phone number not found"); else if(prev==null) { head=head.next; if(head==null) tail=null; System.out.println("Deleted Successfully"); } else { prev.first_name=node.first_name; prev.last_name=node.last_name; prev.phone_number=node.phone_number; prev.city=node.city; prev.gender=node.gender; prev.address=node.address; prev.email=node.email; prev.next=node.next; System.out.println("Deleted Successfully"); } } public void update(String first_name,String phone_number) // method that updates the phone number of person if exists { boolean found=false; Node node=head; while(node!=null) { if(node.first_name.equals(first_name)) { node.phone_number=phone_number; found=true; } node=node.next; } if(!found) System.out.println("No person found with given first name"); else System.out.println("Updated Successfully"); } public void display() // method that displays data in directory { if(head==null) { System.out.println("Empty directory"); return; } System.out.println("People are as follows: "); Node node=head; while(node!=null) { System.out.println(node.toString()); node=node.next; } } public void search(String first_name) // method that searches for person with first name { Node node=head; boolean found=false; while(node!=null) { if(node.first_name.equals(first_name)) { System.out.println(node.toString()); found=true; } node=node.next; } if(!found) System.out.println("No person found with given first name"); } public void sort() // sorts data in linked lists according to first name { Node node1=head; while(node1!=null) { Node node2=node1.next; while(node2!=null) { if(node1.first_name.compareTo(node2.first_name)0) { swap(node1,node2); } node2=node2.next; } node1=node1.next; } System.out.println("Sorted Successfully"); } public void swap(Node n1,Node n2) { String temp=""; temp=n1.first_name; n1.first_name=n2.first_name; n2.first_name=temp; temp=n1.last_name; n1.last_name=n2.last_name; n2.last_name=temp; temp=n1.phone_number; n1.phone_number=n2.phone_number; n2.phone_number=temp; temp=n1.city; n1.city=n2.city; n2.city=temp; temp=n1.address; n1.address=n2.address; n2.address=temp; temp=n1.email; n1.email=n2.email; n2.email=temp; char t=n1.gender; n1.gender=n2.gender; n2.gender=t; } }// prototype of person detailsclass Node{ String first_name,last_name,phone_number,city,address,email; char gender; Node next=null; Node() { } Node(String first_name,String last_name,String phone_number,String city,String address,char gender,String email) { this.first_name=first_name; this.last_name=last_name; this.phone_number=phone_number; this.city=city; this.address=address; this.gender=gender; this.email=email; } public String toString() { return "
First Name: "+this.first_name+"
Last Name: "+this.last_name+"
Phone Number: "+this.phone_number+"
City: "+this.city+ "
Address: "+this.address+"
Gender: "+this.gender+"
Email: "+this.email+"
"; }}

Question

I need an explanation for this program.class Directory{   Node head,tail;   Directory()   {       head=null;       tail=null;   }   public void insert(Node node)           // method that insers node into list if phone number is new   {       Node temp=head;       while(temp!=null && !temp.phone_number.equals(node.phone_number))           temp=temp.next;       if(temp!=null)       {           System.out.println(&#34;Entered phone number already exists&#34;);           return;       }       if(head==null)       {           head=node;           tail=node;       }       else       {           tail.next=node;           tail=node;       }       System.out.println(&#34;Inserted Successfully&#34;);   }   public void remove(String ph_no)                   // method that removes node with given phone number   {       Node prev=null;       Node node=head;       while(node!=null && !node.phone_number.equals(ph_no))       {           prev=node;           node=node.next;       }       if(node==null)           System.out.println(&#34;Phone number not found&#34;);       else if(prev==null)       {           head=head.next;           if(head==null)               tail=null;           System.out.println(&#34;Deleted Successfully&#34;);       }       else       {           prev.first_name=node.first_name;           prev.last_name=node.last_name;           prev.phone_number=node.phone_number;           prev.city=node.city;           prev.gender=node.gender;           prev.address=node.address;           prev.email=node.email;           prev.next=node.next;           System.out.println(&#34;Deleted Successfully&#34;);       }     }   public void update(String first_name,String phone_number)       // method that updates the phone number of person if exists   {       boolean found=false;       Node node=head;       while(node!=null)       {           if(node.first_name.equals(first_name))           {               node.phone_number=phone_number;               found=true;           }           node=node.next;       }       if(!found)           System.out.println(&#34;No person found with given first name&#34;);       else           System.out.println(&#34;Updated Successfully&#34;);   }   public void display()                       // method that displays data in directory   {       if(head==null)       {           System.out.println(&#34;Empty directory&#34;);           return;       }       System.out.println(&#34;People are as follows: &#34;);       Node node=head;       while(node!=null)       {           System.out.println(node.toString());           node=node.next;       }   }   public void search(String first_name)       // method that searches for person with first name   {       Node node=head;       boolean found=false;       while(node!=null)       {           if(node.first_name.equals(first_name))           {               System.out.println(node.toString());               found=true;           }           node=node.next;       }       if(!found)           System.out.println(&#34;No person found with given first name&#34;);   }   public void sort()                           // sorts data in linked lists according to first name   {       Node node1=head;       while(node1!=null)       {           Node node2=node1.next;           while(node2!=null)           {               if(node1.first_name.compareTo(node2.first_name)>0)               {                   swap(node1,node2);               }               node2=node2.next;           }           node1=node1.next;       }       System.out.println(&#34;Sorted Successfully&#34;);   }   public void swap(Node n1,Node n2)   {       String temp=&#34;&#34;;             temp=n1.first_name;       n1.first_name=n2.first_name;       n2.first_name=temp;             temp=n1.last_name;       n1.last_name=n2.last_name;       n2.last_name=temp;             temp=n1.phone_number;       n1.phone_number=n2.phone_number;       n2.phone_number=temp;             temp=n1.city;       n1.city=n2.city;       n2.city=temp;             temp=n1.address;       n1.address=n2.address;       n2.address=temp;             temp=n1.email;       n1.email=n2.email;       n2.email=temp;             char t=n1.gender;       n1.gender=n2.gender;       n2.gender=t;   }  }// prototype of person detailsclass Node{   String first_name,last_name,phone_number,city,address,email;   char gender;   Node next=null;   Node() { }   Node(String first_name,String last_name,String phone_number,String city,String address,char gender,String email)   {       this.first_name=first_name;       this.last_name=last_name;       this.phone_number=phone_number;       this.city=city;       this.address=address;       this.gender=gender;       this.email=email;   }   public String toString()   {       return &#34;
First Name: &#34;+this.first_name+&#34;
Last Name: &#34;+this.last_name+&#34;
Phone Number: &#34;+this.phone_number+&#34;
City: &#34;+this.city+       &#34;
Address: &#34;+this.address+&#34;
Gender: &#34;+this.gender+&#34;
Email: &#34;+this.email+&#34;
&#34;;   }}

Accepted Answer

The given code is used to create a linked list where each node in the list stores a person's…