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 details class 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 "\nFirst Name: "+this.first_name+"\nLast Name: "+this.last_name+"\nPhone Number: "+this.phone_number+"\nCity: "+this.city+ "\nAddress: "+this.address+"\nGender: "+this.gender+"\nEmail: "+this.email+"\n"; } }